Question

cos40*-cos20*+sin10*=0

Answer 1

cos(40)-cos(20)+sin(10)=-2*sin((40+20)/2)*sin((40-20)/2)+sin(10*)=-2*sin(30)*sin((10)+sin(10*)=
-2*0,5*sin(10*)+sin(10*)=-sin(10*)+sin(10*)=0