Answers
Hey there! I'm happy to help!
To find the surface area of a sphere, here is what you do.
You square the radius.
4²=16
You multiply by 4.
16×4=64
And you multiply by pi!
64×π=64π
Therefore, the surface area of the sphere is A. 64π units². It's that easy!
Now you can find the surface area of a sphere! Have a wonderful day! :D
Question :-
What is the surface area of the sphere that has a radius of 4 units?Answer :-
The surface area of the sphere is 64π units².[tex] \rule{180pt}{3pt}[/tex]
Diagram :-
[tex]\setlength{\unitlength}{1.2cm}\begin{picture}(0,0)\thicklines\qbezier(2.3,0)(2.121,2.121)(0,2.3)\qbezier(-2.3,0)(-2.121,2.121)(0,2.3)\qbezier(-2.3,0)(-2.121,-2.121)(0,-2.3)\qbezier(2.3,0)(2.121,-2.121)(-0,-2.3)\qbezier(-2.3,0)(0,-1)(2.3,0)\qbezier(-2.3,0)(0,1)(2.3,0)\thinlines\qbezier (0,0)(0,0)(0.2,0.3)\qbezier (0.3,0.4)(0.3,0.4)(0.5,0.7)\qbezier (0.6,0.8)(0.6,0.8)(0.8,1.1)\qbezier (0.9,1.2)(0.9,1.2)(1.1,1.5)\qbezier (1.2,1.6)(1.2,1.6)(1.38,1.9)\put(0.2,1){\bold{4 \: units}}\end{picture}[/tex]
Solution :-
As per the provided information in the given question, we have been given that the radius of the sphere is 4 units. We have been asked to find or calculate the surface area of the sphere.
To calculate the surface area of the sphere, we will use the formula below :-
[tex]\bigstar \:\:\:\boxed{\sf{\:\:Surface \: Area_{(Sphere)} = 4\pi r^2 \:\:}}[/tex]
Substitute the given values into the above formula and solve for surface area:
[tex]\sf:\implies Surface \: Area_{(Sphere)} = 4\pi r^2[/tex]
[tex]\sf:\implies Surface \: Area_{(Sphere)} = 4 \times \pi \times (4 \: units)^2[/tex]
[tex]\sf:\implies Surface \: Area_{(Sphere)} = (4 \: units)^2 \times 4 \times \pi[/tex]
[tex]\sf:\implies Surface \: Area_{(Sphere)} = 16 \: units^2 \times 4 \times \pi[/tex]
[tex]\sf:\implies \bold{Surface \: Area_{(Sphere)} = 64\pi \: units^2}[/tex]
Therefore :-
The surface area of the sphere is 64π units².[tex]\\[/tex]
Learn more about the surface area of the sphere at https://brainly.com/question/28988747
Have a great day! <33
Related Questions
Please help I did the first 2
Answers
Answer:
x = 1.5
Step-by-step explanation:
6 - 2x = 3
→ Minus 6 from both sides to isolate -2x
-2x = -3
→ Divide -2 from both sides to isolate x
x = 1.5
Sarah has $20 saved. She gets $10 per week for her allowance, and she saves her allowance for the next 3 weeks. At the end of the week, she gets $150 in birthday money. How much money will she have after the 3 weeks? Which of the following sets of equations represents this problem?
Answers
Answer:
$200
Step-by-step explanation:
We know that she already has $20. And we know that every week, for three weeks she gets $10.
20+3(10)+150=m
We add all of this up, and we find that at the end of 3 weeks Sarah has $200 saved.
Select the correct answer. This set of ordered pairs defines a function. {(-49,7), (-56,8), (-63,9), (-70,10)} Which table represents the inverse of the function defined by the ordered pairs? A.
Answers
In the future, you should post all possible answer choices to have a complete post. However, there's enough information to get the answer.
The original set has points in the form (x,y)
The first point is (x,y) = (-49,7) making x = -49 and y = 7. When we find the inverse, we simply swap the x and y values. The inverse undoes the original function and vice versa. So if (-49, 7) is in the original function, then (7, -49) is in the inverse. The rest of the points follow the same pattern.
We end up with this answer
{ (7, -49), (8, -56), (9, -63), (10, -70) }
PLEASE HELP!! what is the equation of a line that is perpendicular to y = 2x + 4 and passes through the point (4, 6)?
Answers
Answer:
The answer is B)
[tex]y = - \frac{1}{2}x + 8[/tex]
Answer:
B. y = -[tex]\frac{1}{2}[/tex]x + 8
Step-by-step explanation:
The line is perpendicular to line whose equation is:
y = 2x + 4 and;
passes through point (4,6) .
The product slopes of two perpendicular lines is -1.
The slope of the line whose equation is y = 2x + 4 is; 2
Let the slope of the perpendicular line (l2) be [tex]m_{l2}[/tex]
[tex]m_{l2} * 2 = -1[/tex]
[tex]m_{l2}[/tex] = [tex]-\frac{1}{2}[/tex]
Taking another point xy on line l2;
[tex]\frac{y - 6}{x - 4} = -\frac{1}{2}[/tex]
Cross multiplying this gives;
y = -[tex]\frac{1}{2}[/tex]x + 8 which is the equation of the perpendicular line!
write each number in scientific notation.
1,050,200
The number between 1 and 10:
The power of 10:
The number in scientific notation:
34,600
The number between 1 and 10:
The power of 10:
The number in scientific notation:
Answers
The number between 1 and 10: 1
The power of 10: 6
The number in scientific notation: 1.05^6 or 1.050200^6
34,600
The number between 1 and 10: 3
The power of 10: 4
The number in scientific notation: 3.46^4
Pregunta N° 1: ¿Cuántas fracciones propias e irreductibles con denominador 24 existen? 1 punto A) 2 B) 4 C) 6 D) 8 E) 10 Pregunta N° 2: ¿Cuántas fracciones impropias e irreductibles con numerador 25 existen? 1 punto A) 19 B) 21 C) 25 D) 29 E) 33 Pregunta N° 3: La edad de Miguel es 4/5 de la edad de su novia. Si las edades de los dos suman 63 años, calcule la edad de la novia de Miguel. 1 punto A) 20 años B) 26 años C) 32 años D) 35 años E) 40 años Pregunta N° 4: Si son las 8 a. m., ¿qué fracción del día ha transcurrido? 1 punto A) 1 B) 2 C) 1/2 D) 1/3 E) 1/5
ayuden porfavor
Answers
Answer:
Pregunta 1: Opcion D. 8
Pregunta 2: Opción A. 19 (aunque lo correcto es decir que son 20)
Pregunta 3: 28 años (no está como opción)
Pregunta 4: Opción D. 1/3
Step-by-step explanation:
Las fracciones irreductibles son aquellas que después de dividirlas por un común divisor, una vez que no se pueden dividir más se dice que son irreducibles, por lo tanto no existe ningún número que sea divisor común del numerador y del denominador más que 1.
Fracciones irreductibles con común denominador 24.
Como máximo divisor tenemos el 24 y como mínimo el 1
entre 1/24 y 1 estarán nuestras fracciones o sea:
1/24 < x/24 < 1. Ahora convertimos el 1 en fracción de 24, lo que sería 24/24 para igualar el numerador en ambos lados de la ecuación, para poder determinar x
1/24 < x/24 < 24/24
Como vemos que x tiene que estar entre 1 y 24, las respuestas serán:
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 y 23
Eliminamos los números divisores de 24, aquellos pares, y nos focalizamos en los que no podriamos dividir por nada con 24, o sea los números primos
5, 7, 11, 13, 17, 19, 23. Como nos falta el 1, obtenemos un total de 8 fracciones: 1/24, 5/24, 7/24, 11/24, 13/24, 17/24, 19/24, 23/24
Mismo procedimiento para el 25:
1/25 es una de las fracciones irreductibles. Pensamos en los valores de x
1/25 < x/25 < 25/25
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25
Los números divisibles por 25, son los multiplos de 5, asi que esas respuestas no irían. Las fracciones irreductibles son:
1/25, 2/25, 3/25, 4/25, 6/25, 7/25, 8/25, 9/25, 11/25, 12/25, 13/25, 14/25, 16/25, 17/25, 18/25, 19/25, 21/25, 22/25, 23/25 y 24/25 haciendo un total de
20. Por alguna razón está mal formulada la pregunta, son 20 pero no está como opción y como te piden fraccion impropia (numerador > denominador), contamos a partir de 26. FIjate que hasta el proximo entero que sería 50/25, también son 20 fracciones (irreductibles e impropias)
26/25, 27/25, 28/25, 29/25, 31/25, 32/25, 33/25, 34/25, 36/25, 37/25, 38/25, 39/25, 41/25, 42/25, 43/25, 44/25, 46/25, 47/25, 48/25, 49/25
Próxima pregunta:
Miguel tiene 4/5 de la edad de la novia, y ambas edades suman 63.
Plantiemos la siguiente ecuacion donde x es la edad de la novia
4/5x + x = 63
9/5x = 63
x = 63 . 5/9 (como 9/5 pasa al otro lado de la igualdad dividiendo, damos vuelta la fraccion multiplicandola)
x = 35
Si la novia tiene 35 años y la edad de Miguel es 4/5 de esa edad
4/5 .35 = (35 .4) /5 = 28
Es raro porque no está la respuesta como tal.
Próxima pregunta:
Al ser las 8 am, quiere decir que han pasado 8 horas de que empezó el día
y el día tiene 24 horas.
8 horas transcurridas / 24 horas totales = 1/3
If Eric can paint $3$ cars in $4$ hours and $2$ trucks in $5$ hours, then how long, in hours, would it take him to paint $4$ cars and a truck? Express your answer as a common fraction.
Answers
Answer:
47/6
Step-by-step explanation:
Given that :
Time taken to paint 3 cars = 4 hours
Time taken to paint 2 trucks = 5 hours
How long will it take him to paint 4 cars and a truck
If 3 cars = 4 hours ;
Then ;
1 car = (4/3)hours
If 2 trucks = 5 hours
Then;
1 truck = (5/2) hours = 2 1/2 hours
Time required To paint 4 cars :
4 × (4/3) = 16/3 hours
Time required to paint 1 truck :5/2 hours
Total time required :
(16/3 + 5/2) = (32 + 15) / 6 = 47/6
4. The rental for a television set changed from $80 per year to $8 per month
What is the percentage increase in the yearly rental?
Answers
Answer:
16%
Step-by-step explanation:
rental charge per year = $80
rental charge at the rate $8 per year = 8 * 12 = 96
the increased amount = 96 - 80 = 16
% = 16 / 100 = 16%
ANSWER QUICKLY PLZZZZZZ ASAP
Answers
Answer:
number 4 on edge
Step-by-step explanation:
Answer:
a. 92 minutes b. 7:56am
Step-by-step explanation:
He should leave at 7:56 so he gets to the bus at 8:05,
he gets to Coventry at 9:37 with enough time to walk 12 minutes to get to work before 10am.
how do you solve this problem ? 4(-3x+1)-3x=71
Answers
Answer:
x = -67/15 = -4-46667
Step-by-step explanation:
4(-3x+1) - 3x = 71
4*-3x + 4*1 - 3x = 71
-12x + 4 - 3x = 71
-15x = 71-4
-15x = 67
x = 67/-15
x = -4.46667
check:
4(-3*-4.46667 + 1) - 3*-4.4666= 71
4(13.4+1) + 13.4 = 71
4*14.4 + 13.4 = 71
57.6 + 13.4 = 71
Hey, please help solve the question.
Answers
Answer:
75%=x-125
90%=x+250
subtract the second from the first
15%=375
100%=?
100%×375/15
100%=2500marked price is 2500
2500+250=2750
90%=2750
100%=?
cost price=3055.56
in the equation z=x^2-3y, find the value of z when x=-3 and y=4
Answers
Answer:
z=-3
Step-by-step explanation:
z=(-3)^2 - 3(4)
z=9 - 12
z=-3
Peter has one of each of the following coins in his pocket: a penny, a nickel, a dime, a quarter, and a half-dollar. Four of these coins are taken out of the pocket and the sum of their values is calculated. How many different sums are possible?
Answers
Answer:
10
Step-by-step explanation:
This is a combinations problem, involving factorials.
5!/3!*2!=5*4/2=20/2=10
The different sum of the 4 coins from the list of 5 coins is an illustration of combination or selection. There are 5 different possible sums.
Given
[tex]n = 5[/tex] --- number of coins
[tex]r = 4[/tex] --- coins to be selected to calculate sum
For the sum of the coin value to be calculated, the 4 coins must be selected. This means combination.
So, we make use of:
[tex]^nC_r = \frac{n!}{(n - r)!r!}[/tex]
This gives
[tex]^5C_4 = \frac{5!}{(5 - 4)!4!}[/tex]
[tex]^5C_4 = \frac{5!}{1!4!}[/tex]
Expand
[tex]^5C_4 = \frac{5*4!}{1*4!}[/tex]
[tex]^5C_4 = \frac{5}{1}[/tex]
[tex]^5C_4 = 5[/tex]
Hence, there are 5 different possible sums.
Read more about combinations at:
https://brainly.com/question/15401733
When the solution of x2 − 9x − 6 is expressed as 9 plus or minus the square root of r, all over 2, what is the value of r? X equals negative b plus or minus the square root of b squared minus 4 times a times c, all over 2 times a 6 42 57 105
Answers
Answer:
The value of r is 105
Step-by-step explanation:
Quadratic equation helps us to solve any quadratic equation. The formula is:
(-b ± √b² - 4ac) ÷ 2a
For the quadratic equation ax²+bx+c
For the equation: X² - 9x - 6:
a = 1, b = -9 and c = -6
Replacing in the quadratic formula:
(-(-9) ± √(-9)² - 4(1*-6)) ÷ 2*1
= 9 ± √105 / 2
That means, the value of r is 105Answer:
105 is right
Step-by-step explanation:
I took the test
CAN ANYBODY HELP ME OUT
Answers
Answer:
Correct option is
b. If two sides and one included angle are equal in triangles PQS and PRS, then their corresponding sides are also equal.
Step-by-step explanation:
Here, we are given the line RQ, which is divided in two equal parts by a line PS which is perpendicular to RQ.
The foot S of PS is on the line RQ.
First of all, let us do a construction here.
Join the point R with P and P with Q.
Please refer to the attached image.
Now, let us consider the triangles PQS and PRS:
Side QS = RS (as given)[tex]\angle PSR = \angle PSQ = 90^\circ[/tex]Side PS = PS (Common side in both the triangles)Now, Two sides and the angle included between the two triangles are equal.
So by SAS congruence we can say that [tex]\triangle PRS \cong \triangle PQS[/tex]
Therefore, the corresponding sides will also be equal.
RP = QP
RP is the distance between R and P.
QP is the distance between Q and P.
Hence, to prove that P is equidistant from R and Q, we have proved that:
b. If two sides and one included angle are equal in triangles PQS and PRS, then their corresponding sides are also equal.
please help i beg plsssssssssz
Answers
Answer:
5/2=20/8=35/14=125/50
Answer:
8, 14, 50
Step-by-step explanation:
5 x 4 = 20
2 x 4 = 8
5 x 7 = 35
2 x 7 = 14
5 x 25 = 125
2 x 25 = 50
Coordinate plane with two lines graphed. The equations of the lines are y equals negative two-thirds x plus four and the other line is y equals two-thirds x. Determine the number of solutions the system of linear equations has and the solution(s) to the equations represented by these two lines? The system of equations has 0 solutions, because the graph has no point of intersection. The system of equations has infinite number of solutions and all real numbers satisfy both equations. The system of equations has 1 solution and it is (3, 2). The system of equations has 1 solution and it is (3, 0).
Answers
Answer:
Step-by-step explanation:
y = -2/3x + 4
y = 2/3x
2/3x = -2/3x + 4
4/3x = 4
4x = 12
x = 3
y = 2/3(3)
y = 2
(3,2) one solution
option 3
9 ÷ (-4 1/2) = L.
What is L.
Answers
Answer:
[tex]\huge\boxed{L = -2}[/tex]
Step-by-step explanation:
L = 9 ÷ [tex](-4 \frac{1}{2} )[/tex]
L = 9 ÷ [tex](-\frac{9}{2} )[/tex]
L = 9 × [tex](-\frac{2}{9} )[/tex]
L = 1× (-2)
L = -2
●✴︎✴︎✴︎✴︎✴︎✴︎✴︎✴︎❀✴︎✴︎✴︎✴︎✴︎✴︎✴︎✴︎✴︎●
Hi my lil bunny!
❧⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯☙
[tex]\boxed {l = \frac{-18}{41} }[/tex]
[tex]\frac{\frac{9}{-41} }{2} = l[/tex]
Simplifies to:
[tex]\frac{-18}{41} = l[/tex]
Let's solve your equation step-by-step.
[tex]\frac{-18}{41} = l[/tex]
Step 1: Flip the equation.
[tex]l = \frac{-18}{41}[/tex]
So your answer would be : [tex]\boxed {l = \frac{-18}{41} }[/tex]
❧⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯☙
●✴︎✴︎✴︎✴︎✴︎✴︎✴︎✴︎❀✴︎✴︎✴︎✴︎✴︎✴︎✴︎✴︎✴︎●
Have a great day/night!
❀*May*❀
You and your friend are playing a game. The two of you will continue to toss a coin until the sequence HH or TH shows up. If HH shows up first, you win. If TH shows up first, your friend wins. What is the probability of you winning?
Answers
Answer:
The probability of friend A winning with HH = 1/4.
Step-by-step explanation:
The probability of an event, A is P(A) given by the relationship;
P(A) = (The number of required outcome)/(The number of possible outcomes)
The parameters given are;
The condition of friend A winning = Coin toss sequence HH shows up
The condition of friend B winning = Coin toss sequence TH shows up
The number of possible outcomes = TT, TH, HH, HT = 4
(TH and HT are taken as different for the game to be fair)
The number of required outcome = HH = 1
Therefore;
The probability of friend A winning with HH = 1/4.
rewrite 1/5:1/2 as a unit rate
Answers
Hey there! I'm happy to help!
The unit rate is how much stuff there is per 1 unit. All ratios can be rewritten as fractions, this one could be 0.2/0.5. The word per means divide, and fractions are basically dividing. So, we want the denominator to be 1.
To get 0.5 to 1, we multiply by 2. So, we will multiply the fraction by 2/2.
0.2/0.5(2/2)=0.4/1
Therefore, the unit rate is 0.4/1 or 0.4:1 or 0.4 per 1.
Have a wonderful day! :D
Mr.Snyder gave his four children $35 to split equally for each car they cleaned out. The children cleaned put 3 cars. Mr.Snyder does not have any coins. He only had dollar bills. How much money should each child get?
Answers
Answer:
$26 for each child
Step-by-step explanation:
35 * 3 = 105 / 4 = 26.25
solve the following: - 3 raised to 1 by 5 the whole raised to 4 (3^1/5)^4
Answers
Answer:
8.30256
Step-by-step explanation:
Step 1: Write out expression
[tex]((-3)^{\frac{1}{5} })^{4(3^{\frac{1}{5} })^4[/tex]
Step 2: Use BPEMDAS to evaluate
[tex](-1.24573)^{4(3^{\frac{1}{5} })^4[/tex]
[tex](-1.24573)^{4(1.24573)^4[/tex]
[tex](-1.24573)^{4(2.40822)[/tex]
[tex](-1.24573)^{9.6329}[/tex]
= 8.30256
And we have our answer!
nine hundred fifty-three thousand nine hundred two
Answers
Answer:
953 902
Step-by-step explanation:
Answer:
953,902
Step-by-step explanation:
nine hundred =900
fifty-three=53
thousand=1000
nine hundred=900
two=2
HELP ASAP WILL MARK BRAINLIEST!!!!!! Use the number line below, where RS=9y+2, ST = 4y+9 and RT = 115. a. What is the value of y? b. Find RS and ST. a. What is the value of y?
Answers
Answer: y = 7
Step-by-step explanation:
The heights of two similar parallelograms are 16 inches and 20 inches. Their
respective areas are (3x+5) square inches and 9x square inches. Find the value of
X?
Answers
Answer: [tex]x=\dfrac{25}{21}[/tex]
Step-by-step explanation:
Area of parallelogram = Base x height
If two parallelograms are similar, then their corresponding sides are proportional.
That means, [tex]\dfrac{\text{Area of first parallleogram}}{\text{Area of second parallleogram}}=\dfrac{\text{height of first parallelogram}}{\text{height of second parallelogram}}[/tex]
[tex]\Rightarrow \dfrac{3x+5}{9x}=\dfrac{16}{20}\Rightarrow \dfrac{3x+5}{9x}=\dfrac{4}{5}\\\\\Rightarrow 5(3x+5)=4(9x)\\\\\Rightarrow\ 15x+25 = 36x\\\\\Rightarrow\ 36x-15x=25\\\\\Rightarrow\ 21x = 25\\\\\Rightarrow\ x=\dfrac{25}{21}[/tex]
Hence, [tex]x=\dfrac{25}{21}[/tex]
a rectangular garden is fenced on all sides with 128 feet of fencing. The garden is 4 feet longer than it is wide. Find the length and width of the garden
Answers
Answer:
Length = 34 feet
Breadth = 30 feet
Step-by-step explanation:
Perimeter= 128 ft
Let the breadth be = [tex]x[/tex]
Let the length be = [tex]x+4[/tex]
∴by the problem ,
2(length+breadth)= perimeter
[tex]2(x+4+x)=128\\2(2x+4)=128\\4x+8=128\\4x=128-8\\4x=120\\x=120/4\\x=30[/tex]
Therefore, length of the garden = 30+4= 34 feet
breadth of the garden = 30 feet
Jorge’s monthly bill from his Internet service provider was $25. The service provider charges a base rate of $15 per month plus $1 for each hour that the service is used. Find the number of hours that Jorge was charged for that month.
Answers
Answer:
10 hours for the month
Step-by-step explanation:
What you know: The total amount Jorge was charged for the month was $25
The base rate is $15
He gets charged $1 per each hour
Setting it up:
15+1h=25
(the 15 is the base rate, plus the 1 dollar per hour (h) which both add to the total of 25 dollars for the month)
Subtract 15 from both sides of the equation to get your variable by itself
1h=10
then divide the 1 on both sides to get h (hours) by itself
h=10
And there's your answer, 10 is the number of hours that Jorge was charged for the month
Hopefully this helped :))
Answer:
10
Step-by-step explanation:
$25 - $15 = $10
and its $1 per hour so the answer is 10hrs
This rectangular patio is tiled using 50 cm by 50 cm square tiles. How many tiles are used?
Answers
Answer:
60 tiles are used
Step-by-step explanation:
1m equals 100 cm.
5m equals 500
3m equals 300
the whole thing is 500 by 300 which when you multiply gives you
150,000. When you multiple 50 by 50 it gives you 2,500. So when you divide 150,000 by 2,500 it gives you a total of 60 tiles. HOPE THIS HELPS
Answer:
60 tiles
Step-by-step explanation:
First, I would convert cm to m to make it easier
50 cm is .5 m
Now we can find how many tiles across it takes to make one row (5m)
.5 goes into 5, 10 times
That means we need 10 tiles across to fill one row
Now we need to find how many tiles it takes to fill up a column (3m)
.5 goes into 3, 6 times
It takes 6 tiles to fill up a column
Now we know it takes 10 tiles across and 6 vertically
10x6=60
60 tiles
7x²-2-3x²
I’m trying to combine like terms
Answers
Final answer if you’re trying to simplify is 4x²-2 because you can’t combine any further.
Answer:
4x^2−2
Step-by-step explanation:
Let's simplify step-by-step.
7x^2−2−3x^2
=7x^2+(−2)+(−3x^2)
Combine Like Terms:
=7x^2(+−2)+(−3x^2)
=(7x^2+(−3x^2))+(−2)
=4x^2+−2
Answer:
=4x2−2
inscribed angles. help asap!
Answers
Answer:
20°
Step-by-step explanation:
The measure of the inscribed angle is equal to the half of the arc it sees
Since AC is the diameter the measure of arc ABC is 180°
and since A sees arc BC and C sees the arc AB
A< + C< = 90° so angle C = 20°
