Question

Demonstrati ca sin 20 grade - sin 160 grade este egal cu cos de 20 de grade + cos de 160 grade

Answer 1

sin160°=sin (180-20)°=sin20°, deci sin20°-sin160°=sin20°-sin20°=0
cos 20°=-cos(180-20)°=-cos20°
deci cos20°+cos160°=cos20°-cos20°=0
asadar 0=0 adevarat

Answer 2

sin160° = sin(180° - 160°) = sin20°

cos160° = - cos(180° - 160°) = - cos20°

Acum, expresia din enunț devine:

sin20° - sin20° = cos20°+(-cos 20°) ⇒ 0 = 0 (Adevărat)