sin 3π/4.sin π/4+cos 3π/4.cos π/4

Bab Trigonometri
Matematika SMA Kelas X

sin (3π/4) . sin (π/4) + cos (3π/4) . cos (π/4)
= 1/2 √2 . 1/2 √2 + (-1/2 √2 . 1/2 √2)
= 2/4 - 2/4
= 0

Sin 3phi/4 . Sin phi/4 + Cos 3phi/4 . Cos phi/4
= Sin 135° . Sin 45° + Cos 135° . Cos 45°
= V2/2 .V2/2 + (-V2/2) . V2/2
= 2/4 + (-2/4)
= 2/4 - 2/4
= 0