find cos 2v and sin 2v when cos v = -5/8 and pi/<v<pi

Answer 1

Step 1:

Trigonometric value is .

Find .

Double - Angle Formulas: .

Substitute in the double angle formula.

Step 2:

Find .

Consider right angle triangle .

From the Pythagorean theorem: .

Substitute and .

Thus, .

Double - Angle Formulas: .

Substitute and in the double angle formula.

Solution :

The values are and