Question

cos20*cos40*cos80= плиз помогите решить

Answer 1

(sin20*cos20*cos40*cos80)/sin20 = (1/2*sin40*cos40*cos80)/sin20 =  (1/4*sin80*cos80)/sin20 = (1/8*sin160)/sin20=(1/8*sin(180-20))/sin20 = (1/8*sin20)/sin20 = 1/8