SOLUTION: Let f and g be the functions defined by f(x)=sin(x) and g(x)=cos(x). For which of the following values of a is the tangent line to f at x=a parallel to the tangent line to g at x=a

Question 1050262: Let f and g be the functions defined by f(x)=sin(x) and g(x)=cos(x). For which of the following values of a is the tangent line to f at x=a parallel to the tangent line to g at x=a?
Answer by robertb(5830) (Show Source): You can put this solution on YOUR website!
f(x)=sin(x) and g(x)=cos(x) ===> f'(x)=cos(x) and g'(x)= -sin(x).
We want f'(a) = g'(a), or cos(a) = -sin(a).
<===> cos(a) + sin(a) = 0.
===>
<===> , or
====> , where k = ..., -2,-1, 0, 1, 2, 3,.... .
====>
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