Question

Nilai dari sin40 x sin20 x cos10 adalah

Answer 1

Sin 40.sin20.cos 10
= (1/2.2.sin40.sin20)cos10
={1/2 [cos(40+20)-cos(40-20)]}cos10
={1/2cos60+1/2cos20}cos 10
=1/2 cos60cos 10+ 1/2 cos20cos10
=1/4(cos70+cos50)+(1/4cos30+cos10)