If cos (-) = 4/5 , 0 < (-) < pie/2

find the exact value of

(a) sin 2(-)

(b) sin 4(-)

given that tan x = square root of 11 all over 3, o < x < pie/2 , find the exact value of sin x

If anyone could help me with these questions id be gratefull

edit : damn.. can anyone help me show that sin (2x + x) = 3sin x - 4sin(to the power of 3)x