求∫[0,a]x^2/√(x^2+a^2)dx详细过程
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x = a tanθ
dx = asec^2θdθ
∫[0,a]x^2/√(x^2+a^2)dx
= ∫[0,pi/4]a^2 tan^2θ secθdθ
= ∫[0,pi/4]a^2 (sec^3θ - secθ)dθ
= a^2 [-(1/2)(ln(secθ + tanθ)) + (1/2)(secθ + tanθ)] θ from 0 to pi/4
= a^2/2 [-ln(√2 + 1) + √2 ]
dx = asec^2θdθ
∫[0,a]x^2/√(x^2+a^2)dx
= ∫[0,pi/4]a^2 tan^2θ secθdθ
= ∫[0,pi/4]a^2 (sec^3θ - secθ)dθ
= a^2 [-(1/2)(ln(secθ + tanθ)) + (1/2)(secθ + tanθ)] θ from 0 to pi/4
= a^2/2 [-ln(√2 + 1) + √2 ]
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