- #1
aglo6509
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Homework Statement
∫cos^3(x)dx
Homework Equations
http://college.cengage.com/mathemat...students/derivatives/derivative_integrals.pdf
http://college.cengage.com/mathemat...ytic/8e/students/trig_review/trigonometry.pdf
This is the website I've using to get my formulas.
The Attempt at a Solution
This seems to be an easy problem but I can't the answer.
Heres my attempt:
∫cos^3(x)dx
∫cosxcos^2(x)dx
∫cosx((1+cos2x)/2) dx
∫(cosx + (cosxcos2x))/2 dx
∫(cosx)/2dx + ∫(cosxcos2x)/2 dx
-1/2sinx + ∫1/2(cos(-x)+cos3x)dx <---double angle formula
-1/2sinx + 1/2[sin(-x) - 1/3sin3x] +C
I thought this was right, but the answer they give in the back of my exam review packet is:
sinx-(sin^3(x))/3 +C
I can't think of anyway of getting a sin^3! Please help