Question

68cos^2 (5п/6)-68sin^2(5п/6)

Answer 1

$68cos^2 (frac{5pi}{6}) -68sin^2(frac{5pi}{6} )=68(cos^2(frac{5pi}{6}) -sin^2(frac{5pi}{6} ))=68cos(2*frac{5pi}{6} )= \ \ =68cos(frac{5pi}{3} )=68cos(frac{6pi-pi}{3})=68cos(2pi-frac{pi}{3} )=68cos(frac{pi}{3})= \ \ =68* frac{1}{2}=34$