The angle between a diagonal and the longer base of the isosceles trapezoid MNFD is 45°. NK is an altitude to the longer base. If MD = 9 and NF = 5, find:
- NK
- MK
- MF
- [tex]A_{AMNFD}[/tex]

Answer:

[tex]NK \approx 7.001[/tex], [tex]MK = 2[/tex], [tex]MF \approx 7.001[/tex], [tex]A_{AMNFD} = 49.007[/tex]

Step-by-step explanation:

According to the statement, we find the following inputs:

[tex]\angle MDK = \angle DMF = 45^{\circ}[/tex] (Due to the condition of isosceles trapezoid)

[tex]MD = 9[/tex]

[tex]NF = 5[/tex]

Given than longer base and shorter base are parallel to each other, we conclude that:

[tex]\angle KND = 180^{\circ} -\angle NKD - \angle KDN[/tex]

[tex]\angle KND = 180^{\circ}-90^{\circ}-45^{\circ}[/tex]

[tex]\angle KND = 45^{\circ}[/tex]

[tex]\angle FND = 90^{\circ}-\angle KND[/tex]

[tex]\angle FND = 45^{\circ}[/tex] (By definition of complementary angles)

[tex]\angle FND = \angle NFM = 45^{\circ}[/tex] (Due to the condition of isosceles trapezoid)

[tex]\angle MDK = \angle DMF = \angle FND = \angle NFM = 45^{\circ}[/tex]

[tex]\angle NOF = \angle MOD = \angle MOF = \angle FOD = 90^{\circ}[/tex] (By definitions of complementary and vertical angles and the theorem that states that sum of internal angles within a triangle equals 180º)

[tex]MO = DO = \frac{\sqrt{2}}{2}\cdot MD[/tex] (By theorem for 45-45-90 Right Triangle)

[tex]NO = OF = \frac{\sqrt{2}}{2}\cdot NF[/tex] (By theorem for 45-45-90 Right Triangle)

If we know that [tex]MD = 9[/tex] and [tex]NF = 5[/tex], then we find that:

[tex]DO = MO \approx 6.364[/tex]

[tex]NO = OF \approx 3.536[/tex]

The value of MK is obtained from the following relationship:

[tex]MK = \frac{MD-NF}{2}[/tex]

[tex]MK = \frac{9-5}{2}[/tex]

[tex]MK = 2[/tex]

And the value of KD is calculated from this expression:

[tex]KD = MD-MK[/tex]

[tex]KD = 9-2[/tex]

[tex]KD = 7[/tex]

Now by the Pythagorean Theorem we find that:

[tex]NK = \sqrt{(NO+DO)^{2}-KD^{2}}[/tex]

[tex]NK = \sqrt{9.9^{2}-7^{2}}[/tex]

[tex]NK \approx 7.001[/tex]

And considering the symmetry characteristics of an isosceles trapezoid, we determine MF:

[tex]MF = NO + DO \approx 7.001[/tex]

Lastly, the area of the isosceles trapezoid is determined by the following formula:

[tex]A_{AMNFD} = NF\cdot NK + MK\cdot NK[/tex]

[tex]A_{AMNFD} = NK\cdot (NF+MK)[/tex]

If we know that [tex]NK \approx 7.001[/tex], [tex]NF = 5[/tex] and [tex]MK = 2[/tex], then the area of the figure is:

[tex]A_{AMNFD} = (7.001)\cdot (5+2)[/tex]

[tex]A_{AMNFD} = 49.007[/tex]

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