Question

Mengapa cos 90 = 0 , jawaban harus disertai alasan

Answer 1

90 = 45 + 45
cos 90 = cos (45 + 45) 
cos 45 cos 45 - sin 45 sin 45
= cos² 45 - sin² 45
= (1/2 √2)² - (1/2 √2)²
= 1/2 - 1/2
= 0