Maths唔識抵死題(16/9)

cos(x/2) = 3/4
Hypothenue = 4,
The oppoisite side = (4^2 - 3^2)^(1/2) = 7^(1/2)
sin(x/2) = √7/4
sinx = 2sin(x/2)cos(x/2)
= 2(√7/4)(3/4)
= 3√7/8
cosx = cos^2 (x/2) - sin^2 (x/2)
= (3/4)^2 - (√7/4)^2
= 9/16 - 7/16
= 2/16