Question

If cosA =1/3, then find the value of cos 2A.

Answer 1

Step-by-step explanation:

cos2A=cos(A+A)

cosacosb-sinasina

1/3x1/3-2root2/3x2root2/3

1/9-8/9

-7/9 is the answer of this question

Answer 2

cos(2A) = 2cos^2(A) - 1

= 2(1/3)^2 - 1

= 2(1/9) - 1

= 2/9 - 1

= -7/9