Упростить: cos40° cos20°

Question

Упростить: cos40° cos20°

Answer 1

Решение
Упростить:
cos40° cos20° = 1/2[cos(40° - 20°) + cos(40° + 20°) ] =
= 1/2[cos20° + cos60°] = (1/2)*cos20° + 1/4