A geometry problem by Yahia El Haw

Geometry Level 3

The parallelogram shown in the figure below has a perimeter of 44 cm and an area of 64 cm 2 ^2 . Find angle T in degrees.


The answer is 34.80.

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4 solutions

Yahia El Haw
Nov 8, 2016

Since the perimeter is the sum of the side lengths, we have

44 = 2 ( 3 x + 2 ) + 2 ( 5 x + 4 ) 44=2(3x+2)+2(5x+4)

44 = 6 x + 4 + 10 x + 8 44=6x+4+10x+8

x = 2 x=2

Therefore, 3 x + 2 = 8 3x+2=8 and 5 x + 4 = 14 5x+4=14 .

The area of a parallelogram is a b sin θ ab~\sin \theta where a a and b b are two adjacent sides and θ \theta is the included angle. We have

64 = 8 ( 14 ) ( sin T ) 64=8(14)(\sin T)

sin T = 4 7 \sin T=\dfrac{4}{7}

T = sin 1 34.8 5 T=\sin^{-1} \approx \boxed{34.85^\circ}

The parameter is given by:

2 ( 3 x + 2 + 5 x + 4 ) = 44 16 x + 12 = 44 x = 2 \begin{aligned} 2(3x+2 + 5x+4) & = 44 \\ 16 x + 12 & = 44 \\ \implies x & = 2\end{aligned}

The area is given by:

( 3 x + 2 ) ( 5 x + 4 ) sin ( T ) = 64 ( 6 ) ( 14 ) sin ( T ) = 64 sin ( T ) = 4 7 T = 34.850 \begin{aligned} (3x+2)(5x+4)\sin(T) & = 64 \\ (6)(14)\sin(T) & = 64 \\ \sin(T) & = \frac 47 \\ \implies T & = \boxed{34.850}^\circ \end{aligned}

From the perimeter, solve for x x , we have

44 = 2 ( 3 x + 2 ) + 2 ( 5 x + 4 ) 44=2(3x+2)+2(5x+4) \implies 44 = 6 x + 4 + 10 x + 8 44=6x+4+10x+8 \implies x = 2 x=2

The sides therefore area 3 ( 2 ) + 2 = 8 3(2)+2=8 and 5 ( 2 ) + 4 = 14 5(2)+4=14 . Now using the formula: A = a b sin θ A=ab \sin \theta where a a and b b are side lengths and θ \theta is the included angle, we have

64 = 14 ( 8 ) sin T 64=14(8) \sin~T

sin T = 4 7 \sin~T=\dfrac{4}{7}

T = sin 1 4 7 = 34.8 5 T=\sin^{-1}\dfrac{4}{7}=34.85^\circ

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