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∫sinn(x)cosm(x)dx
If n is odd or if m is odd, then we can use the identity sin2(x)+cos2(x)=1 to manipulate the integral into the form ∫sink(x)cos(x)dx which can be solved with the substitution u=sin(x); or into the form ∫sin(x)cosk(x)dx which can be solved with the substitution u=cos(x).
If n and m are both even, though, this doesn't work and we need to use the double angle formulas sin2(x)=12(1−cos(2x)), or cos2(x)=12(1+cos(2x)) to simplify the problem.
- ∫tann(x)secm(x)dx,
If n is odd or m is even we can use the identity tan2(x)+1=sec2(x) to manipulate the integral into the form ∫tank(x)sec2(x)dx which can be solved with the substitution u=tan(x); or into the form ∫tan(x)seck(x)dx which can be solved with the substitution u=sec(x).
If neither works, then there may be a way to simplify the problem using integration by parts, but it's likely to be hard.
- ∫sin(ax)sin(bx)dx
There are two methods: one is to integrate by parts twice; the other is to use addition-of-angle formulas.
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