Question

If sin theta = -(sqrt(3))/2 and pi < =theta <= (3pi)/2, determine the value of cos(20)

Answer 1

Sin theta = -1/2

Explanation:

pi < =theta <= (3pi)/2.

The above expression shows we are dealing with angle on the 3rd quadrant.

I.e greater than 180 but less than 270.

So sin tita = (√3)/2

But sin and cos are all negative in the third quadrant.

So tita = sin^-1(√3)/2

tita = 60°

Cos tita = cos 60

Cos tita = cos 60

Cos60 = 0.5

Cos 60 = 1/2

If

sin theta = -(sqrt(3))/2

Sin theta = -1/2