Тригонометрия 10кл. решить , ! cos20°×cos40°×sin10°=

1/2*(cos(40-20)+cos(40+20))*sin10=
=1/2(cos20+cos60)*sin10=1/2*cos20sin10+1/4*sin10=
=1/2*1/2*(sin(10-20)+sin(10+20)+1/4*sin10=
=-1/4*sin10+1/4*sin30+1/4*sin10=1/4*1/2=1/8