diketahui cos a = 0.8 untuk 0 <2a < 2π nilai tan 2a?

Bab Trigonometri
Matematika SMA Kelas X

cos a = 0,8 = 8/10 = x/r

y = √(r² - x²)
y = √(10² - 8²)
y = √(100 - 64)
y = 6

tan 2a
= (2 tan a) / (1 - tan² a)
= (2 . y/x) / (1 - (y/x)²)
= (2 . 6/8) / (1 - (6/8)²)
= (3/2) / (1 - 36/64)
= (3/2) / ((64 - 36)/64))
= (3/2) / (28/64)
= 3/2 x 64/28
= 24/7
= 3 3/7