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2020-01-08
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原式=∫x^2/√[x(1-x)]dx
=∫x^(3/2)/√(1-x)dx
令t=√(1-x),则x=1-t^2,dx=-2tdt
原式=∫[(1-t^2)^(3/2)]/t*(-2t)dt
=-2∫(1-t^2)^(3/2)dt
令t=sinu,则dt=cosudu
原式=-2∫cos^3u*cosudu
=-2∫cos^4udu
=-(1/2)*∫(2cos^2u)^2du
=-(1/2)*∫(1+cos2u)^2du
=-(1/2)*∫[1+2cos2u+cos^2(2u)]du
=-(1/2)*[u+sin2u]-(1/4)*∫(1+cos4u)du
=-(1/2)*[u+sin2u]-(1/4)*[u+(1/4)*sin4u]+C
=(-3/4)*u-(1/2)*sin2u-(1/16)*sin4u+C
=(-3/4)*arcsint-t√(1-t^2)-(1/8)*sin2ucos2u+C
=(-3/4)*arcsint-t√(1-t^2)-(1/4)*sinucosu(cos^2u-sin^2u)+C
=(-3/4)*arcsint-t√(1-t^2)-(1/4)*t√(1-t^2)*(1-2t^2)+C
=(-3/4)*arcsin√(1-x)-√(x-x^2)-(1/4)*√(x-x^2)*(2x-1)+C
=(-3/4)*arcsin√(1-x)-(1/4)*(3+2x)*√(x-x^2)+C,其中C是任意常数
=∫x^(3/2)/√(1-x)dx
令t=√(1-x),则x=1-t^2,dx=-2tdt
原式=∫[(1-t^2)^(3/2)]/t*(-2t)dt
=-2∫(1-t^2)^(3/2)dt
令t=sinu,则dt=cosudu
原式=-2∫cos^3u*cosudu
=-2∫cos^4udu
=-(1/2)*∫(2cos^2u)^2du
=-(1/2)*∫(1+cos2u)^2du
=-(1/2)*∫[1+2cos2u+cos^2(2u)]du
=-(1/2)*[u+sin2u]-(1/4)*∫(1+cos4u)du
=-(1/2)*[u+sin2u]-(1/4)*[u+(1/4)*sin4u]+C
=(-3/4)*u-(1/2)*sin2u-(1/16)*sin4u+C
=(-3/4)*arcsint-t√(1-t^2)-(1/8)*sin2ucos2u+C
=(-3/4)*arcsint-t√(1-t^2)-(1/4)*sinucosu(cos^2u-sin^2u)+C
=(-3/4)*arcsint-t√(1-t^2)-(1/4)*t√(1-t^2)*(1-2t^2)+C
=(-3/4)*arcsin√(1-x)-√(x-x^2)-(1/4)*√(x-x^2)*(2x-1)+C
=(-3/4)*arcsin√(1-x)-(1/4)*(3+2x)*√(x-x^2)+C,其中C是任意常数
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