Jika diketahui cos 20° = a, maka nilai dari cos 70° cos 50° =
Cos(70+50)+cos(70-50)
=cos120+cos20
=cos120+a
=6cos20+a
=6a+a
=7a
Jika diketahui cos 20° = a, maka nilai dari cos 70° cos 50° =
Cos(70+50)+cos(70-50)
=cos120+cos20
=cos120+a
=6cos20+a
=6a+a
=7a