Let, I=inttan^8xdx=inttan^6x(sec^2x-1)d,I=∫tan8xdx=∫tan6x(sec2x−1)d,
=int(tanx)^6d(tanx)-inttan^4x(sec^2x-1)dx,=∫(tanx)6d(tanx)−∫tan4x(sec2x−1)dx,
=tan^7x/7-int(tanx)^4d(tanx)+inttan^2x(sec^2x-1)dx,=tan7x7−∫(tanx)4d(tanx)+∫tan2x(sec2x−1)dx,
=tan^7x/7-tan^5x/5+int(tanx)^2d(tanx)-inttan^2xdx,=tan7x7−tan5x5+∫(tanx)2d(tanx)−∫tan2xdx,
=tan^7x/7-tan^5x/5+tan^3x/3-int(sec^2x-1)dx.=tan7x7−tan5x5+tan3x3−∫(sec2x−1)dx.
:. I=tan^7x/7-tan^5x/5+tan^3x/3-tanx+x+C.
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