Local linearization

[Mirole]

f(x) = cosx, a = \pi/2
since, L(x)=f'(x)(x-a) -f(a)
f'(x) = -sinx
= -sin(\pi/2)(x-\pi/2) - f(a)


I'm stuck as to where to go next, is this even right?

[Mirole]

Nevermind, I got it to be -x+\pi/2, which is correct!