∫ xsinx/cos³x dx
= ∫ xsec²xtanx dx
= ∫ xsecx dsecx
= (1/2)∫ x dsec²x
= (1/2)xsec²x - (1/2)∫ sec²x dx
= (1/2)xsec²x - (1/2)tanx + C
= (1/2)(xsec²x - tanx) + C
∫ xsinx/cos³x dx
= ∫ xsec²xtanx dx
= ∫ xsecx dsecx
= (1/2)∫ x dsec²x
= (1/2)xsec²x - (1/2)∫ sec²x dx
= (1/2)xsec²x - (1/2)tanx + C
= (1/2)(xsec²x - tanx) + C