Sonia G.

asked • 02/20/17

Trigonometry- Area of Quadrilateral

Find area of quadrilateral ABCD with AB= 12cm, BC=10 cm, and CD=10 cm, angle B = 108 degres, and angle C = 132 degrees.

Sonia G.

Is this quadrilateral a trapezoid?
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02/20/17

Sonia G.

How do you calculate angle ABD?
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02/20/17

Sonia G.

The parallel sides are CB (10 cm long) and DA.
How would you calculate angle DBC?
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02/20/17

Sonia G.

I don't know how to use the Law of Sines in a quadrilateral (trapezoid) to calculate angle DBC.
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02/20/17

Mark M.

sin 132 / d = sin DBC / 10
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02/20/17

Sonia G.

Could you pinpoint where I am making a mistake?
 
Triangle 1- (0.5)(10)(10)(sin 32)
Triangle 2- (0.5)(12)(18.27)(sin 156)
 
18.27 is the length of "d", which is calculated from the law of cosine: d2 = 100 + 100 - 2(10)(10)(cos 132)
156 is the measurement of angle ABD, which is (180 - angle DBC), and angle DBC is calculated from law of sine: (sin 132/18.27) = (sin DBC/10)
 
Your help is greatly appreciated
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02/20/17

Sonia G.

Would you pinpoint my mistake?
 
Area of Triangle 2- (0.5)(12)(18.27)(sin 24)
 
18.27 is "d"
24 is angle DBC
 
Your help is greatly appreciated.
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02/20/17

2 Answers By Expert Tutors

By:

Doug C. answered • 02/21/17

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Mark M. answered • 02/20/17

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Mathematics Teacher - NCLB Highly Qualified

Sonia G.

Is this quadrilateral a trapezoid?
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02/20/17

Mark M.

I do not have enough information to determine.
What values did you determine?
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02/20/17

Sonia G.

I only have 132 degrees and 108 degrees. When drawing and labeling a diagram, I get a trapezoid.
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02/20/17

Sonia G.

How do you calculate angle ABD?
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02/20/17

Mark M.

Which two sides are parallel?
m∠ABD = 108° - m∠DBC
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02/20/17

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