Question

求助数学达人第一题和第三题，怎么才能解出来

Answer 1

∫1/(1+sinx)dx
=∫[(1-sinx)/(1-sinx)(1+sinx)]dx
=∫(1-sinx)/(1-sin^2 x)dx
=∫[(1-sinx)/cos^2 x]dx
=∫[1/cos^2 x]dx+∫[1/cos^2 x]d(cosx)
=∫[(sin^2 x+cos^2 x)/cos^2 x]dx-(1/cosx)
=∫[sin^2 x/cos^2 x]dx+x-(1/cosx)
=-∫[sinxd(cosx)]/cos^2 x+x-(1/cosx)
=∫sinxd[1/cosx]+x-(1/cosx)
=(sinx/cosx)-∫[1/cosx]cosxdx+x-(1/cosx)
=tanx-x+x-(1/cosx)+C
=(sinx-1)/cosx+C

追答

∫1/(1+tanx)dx
=∫1/(1+sinx/cosx)dx
=∫cosx/(cosx+sinx)dx
=∫cosx(cosx-sinx)/(cosx+sinx)(cosx-sinx)dx
=∫(cos²x-sinxcosx)/(cos²x-sin²x)dx
=[∫(1+cos2x-sin2x)/cos2xdx]/2
=[∫(1+cos2x-sin2x)/cos2xd2x]/4
=(∫sec2xd2x+∫d2x+∫tan2xd2x)/4
=ln|sec2x+tan2x|/4+x/2+ln|cos2x|/4+C
=x/2+ln|cos2x(sec2x+tan2x)|/4+C
=x/2+ln(1+sin2x)/4+C