不定积分∫√(9-x^2)dx

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不定积分∫√(9-x^2)dx

不定积分∫√(9-x^2)dx
不定积分∫√(9-x^2)dx

不定积分∫√(9-x^2)dx
令x=3sint,则dx=3costdt.
t=arcsin(x/3).sin2t=2sintcost
∫√(9-x^2)dx=∫[√(9-9sin²t)]3(cost)dt=∫9cos²tdt=9∫(1/2)[1+cos(2t)]dt=9∫(1/4)[1+cos(2t)]d(2t)
=(9/4)[2t+sin2t]+C,(C为任意常数).
∫√(9-x^2)dx=(9/4)[2arcsin(x/3)+2(x/3)√(1-(x/3)²)]+C
=(9/2)arcsin(x/3)+(1/2)x)√[(3²-(x²)]+C,(C为任意常数).