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