解ï¼åå¼=3â«x²â1-x
令â1-x=t
x=1-t²
dx=-2tdt
åå¼=3â«ï¼1-t²ï¼²t(-2t)dt
=3â«ï¼-2t²+4t^4-2t^6ï¼dt
=-6â«t²dt+12â«t^4dt-6â«t^6dt
=-2t^3+12/5t^5-6/7t^7+c
=-2â(1-x)^3+12/5â(1-x)^5-6/7â(1-x)^7+cã
â«ï¼1-3xï¼^6dx
=(-1/3)â«(1-3x)^6d(1-3x)
=-1/3*(1-3x)^7*(1/7)+C
=-1/21*ï¼1-3xï¼^7+Cã
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