Question

Is this correct?

Question: Write the equation of the line that represents the linear approximation to
f(x) = sin(x) at pi/4. Estimate f(0.75) using linear approximation.

My answer:
a) y = cos(pi/4)(pi/4 - pi/4) + sqrt(2)/2
b) y = (sqrt(2)/2)(0.75 - pi/4) + sqrt(2)/2