## Elementary Geometry for College Students (6th Edition)

Let take angle A as α in parallelogram ABCD therefore cos α = $\frac{length of adjacent}{length of hypotenuse}$ cos α = $\frac{10 - 7}{8}$ = $\frac{3}{8}$ therefore α = $cos^{-1}$($\frac{3}{8}$) = 68° so angle A = 68°