Question

If cos x=−6/7, and 90°

Answer 1

Answer: 0.4693877

Explanation:

Given that:

cos x=−6/7,

From trigonometry :

Cosx + sinx = 1

Cos2x = cos(x + x)

Recall the double angle identity:

Cos2x = 2cos^2x - 1

Sin2x = 1 - 2sin^2x

Since cosx = - 6/7

Then

Cos2x = 2cos^2x - 1

Cos2x = 2cosx^2 - 1

Cos2x = 2(-6/7)^2 - 1

Cos2x = 2(36/49) - 1

Cos2x = 2 * (72/98) - 1

Cos2x = (2 * 0.7346938) - 1

Cos 2x = ( 1.4693877 - 1)

Cos2x = 0.4693877