Prove that limit X approaches a from the right : cos x= cos a

Answer 1

This question has been answered before on Wyzant by Andy C. (answered • 10/15/18)

I quote:

Difference quotient

{ cos(a+x)-cos(x)} / (a+x-x)

cos(a+x)-cos(x) / a = 0

so the derivative exists which guarantees continuity.

So cos x = cos a as x--> a