Differentiate the following functions with respect to x :
cos(x+a)
We have,
ddx{cos(x+a)}
=ddx{cos x.cos a−sin x.sin a}
[∵ cos (x+a)=cos x cos a−sin x sin a]
=cos addx(cos x)−sin a−ddx(sin x)
=cos a(−sin x)−sin a (cos x)
=cos x sin a+sin x+cos a
=−(sin x cos a+cos x sin a)
=−sin (x+a)