Question

21•cos177 градусов/cos3 градусов

Answer 1

$dfrac{21cdotcos177а}{cos3а} = dfrac{21cos(180а-3а)}{cos3а}= dfrac{21cdot(-cos3а)}{cos3а}=-21$

Answer 2

21cos177/cos3=21*cos(90+87)/cos(90-87)=21*(-sin87)/sin87=-21