Question

∫x^2/(1-x^2)dx 求积分

还有个 ∫1/(sin2xcosx)dx 求 积分

Answer 1

解：∫x^2/(1-x^2)dx=∫[1/(1-x^2)-1]dx
=∫[(1/2)/(1+x)+(1/2)/(1-x)-1]dx
=(1/2)ln│(1+x)/(1-x)│-x+C (C是积分常数)；
∫1/(sin2xcosx)dx=∫dx/(2sinxcos²x)
=(1/2)∫sinxdx/(sin²xcos²x)
=(-1/2)∫d(cosx)/[(1-cos²x)cos²x]
=(-1/2)∫[(1/2)/(1+cosx)+(1/2)/(1-cosx)+1/cos²x]d(cosx)
=(-1/2)[(1/2)ln│(1+cosx)/(1-cosx)│-1/cosx]+C (C是积分常数)
=(1/2)[ln│(1-cosx)/sinx│+1/cosx]+C。