cos 35˚ cos 20˚ + sin 35˚ sin 20˚ =

cos (35 - 20) = cos 15 = cos( 45-30) = cos45.cos30 + sin45.sin30 = selanjutnya hitung sendiri

cos(35-20) =cos 15
cos 15 = cos (45-30)
= cos a cos b + sin a sin b
= cos 45 cos 30 + sin 45 sin 30
= 1/2√2 . 1/2√3. + 1/2√2 . 1/2
= 1/4√6 + 1/4√2
= 1/4 (√6+√2

hehe maaf ya kalo salah