cosx12 cosx12Solution cos x 12 cos x 12 expanding cos x

(cosx+1)^2 - (cosx-1)^2

( cos x + 1)^2 - ( cos x - 1)^2

expanding (cos x + 1)^2 we get

cos^2x + 2 cos x + 1

expanding ( cos x -1 )^2 we get

cos^2 x - 2cos x + 1

therefore, expression becomes

cos^2x + 2 cos x + 1 - ( cos^2 x - 2cos x + 1) = cos^2x + 2 cos x + 1 - cos^2 x + 2 cos x -1

= 4 cos x