Posted by **Julie** on Thursday, April 12, 2012 at 12:28am.

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

- Calculus grade 12 -
**Reiny**, Thursday, April 12, 2012 at 7:45am
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**, Thursday, April 12, 2012 at 11:52am
Thanks Reiny, I have checked it over and it seems about right to me. Thank you.

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