The longer diagonal divides the parallelogram into two triangles, each with measures of side equal to:
28,42,58.
Use the cosine rule to find the angles, A, B and C:
c²=a² + b² -2ab*cos(C)
Note that cos(θ)<0 for 90°<θ<180°.
The measures of two sides of a parallelagram are 28 in and 42 in. If the longer diagonal has measure 58 in, find the measures of the angles at the vertices
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