Решение:sin10*sin50*sin70

Дано:

sin10 = cos80

sin50 = cos40

sin70 = cos20

Ответ:

cos20 * cos40 * cos80 = (2sin20 * cos20 * cos40 * cos80) / (2sin20) =

= (sin40 * cos40 * cos80) / (2sin20) =

= (sin80 * cos80) / (4sin20) =

= (sin160) / (8sin20) =

= 1 / 8

sin160 = sin20