urgent help please.

Question

Use the angle difference identity to find the exact value of each;

3) cos 75 °.

4)105 °.

8) Solve cos 2 θ = cos θ + 2 for 0 < θ < 2p

Answer 1

(3)

Step 1:

The trigonometric value is .

Rewrite value as .

Since  .

Substitute the values of  and .

Solution :

.

Answer 2

(4)

Step 1:

The trigonometric value is .

Rewrite value as .

Since  .

Substitute the values of  and .

Solution :

.

Answer 3

(8)

Step 1:

The trigonometric expression is .

Use the trigonometric identity .

The range of  is .

So .

.

Step 2:

The general solution of is ,where is integer.

.

if then .

if then

is out of the interval .

The solution of the trigonometric expression is in the interval .

Solution :

The solution of the trigonometric expression is  .