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September 1, 2014

September 1, 2014

Posted by **Anonymous** on Tuesday, November 15, 2011 at 10:07pm.

- geometry -
**MathMate**, Tuesday, November 15, 2011 at 10:14pmSo we have a trapezoid ABCD, in which

AB=unknown

BC=10,

CD=14

DA=10

and

AC=16.

Sketch the triangle ACD for which the lengths of all three sides are known.

Using the cosine rule, calculate the cosine of A using

cosA=(AC²+AD²-CD²)/(2*AC*AD)

and hence calculate ∠A.

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