Question

cos 2a =? options: a) cos^2 a+1 b) cos^2 a-1 c) 2cos^2 a+1 d) 2cos^2 a-1​

Answer 1

Answer:

(d)

Step-by-step explanation:

cos (a+a) = cos a . cos a - sin a . sin a

or,cos (a+a) = cos^2 a - sin^2 a

or, cos (a+a) = cos^2 a - (1- cos^2 a)

or,cos (a+a) = 2 cos^2 a - 1