Доказать,что sin10*xcos20*xcos40*=1/8

Question

Доказать,что sin10*xcos20*xcos40*=1/8

Answer 1

Cos10*sin10*cos20*cos40/cos10=sin20*cos20*cos40/(2cos10)=
=sin40*cos40/(4cos10)=sin80/(8cos10)=sin(90-10)/(8cos10)=
=cos10/(8cos10)=1/8