Posted by Julie on .
Determine the equation of the tangent line to the function (² = square): f(x) = x + cos²x at x = pie/4

Calculus grade 12 
Reiny,
f'(x) = 1+ 2cosx(sinx)
f(π/4) = π/4 + cos^2 (π/4) = π/4 + 1/2 = (2+π)/4
f'(π/4) = 1 + 2(1/√2)(1/√2) = 1  2/2 = 0
so the line is horizontal and its equation is simply
y = (2+π)/4
check my arithmetic, (did not write it down first) 
Calculus grade 12 
Julie,
Thanks Reiny, I have checked it over and it seems about right to me. Thank you.