Question

Найдите значение выражения  $frac{15(sin ^{2}21^{0}-cos ^{2}21^{0})}{cos42^{0}}$

Answer 1

$frac{15(sin ^{2}21-cos ^{2} 21) }{cos42} = frac{-15(cos ^{2} 21-sin ^{2} 21) }{cos42} = frac{-15*cos42}{cos42} =-15$