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Answers for “如何积分 $x^3\sqrt{1+x^4}$?”

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To evaluate the definite integral, substitute x=1+eux = 1 + e^u, which gives dx=eududx = e^u du. Convert the bounds from u=0u=0 and u=ln⁡2u=\ln 2 to x=2x=2 and x=3x=3.

Conditions: The integral is definite with bounds u=0u=0 to u=ln⁡2u=\ln 2.; The integrand is eu1+eue^u \sqrt{1+e^u}.; Substitution x=1+eux = 1 + e^u is used.

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The substitution works because the derivative of 1+x41+x^4 is 4x34x^3, which matches the x3x^3 term present in the integrand x31+x4x^3\sqrt{1+x^4}. This allows the integral to be transformed into a simpler power function form, enabling the calculation of the antiderivative required for the integration by parts step.

Conditions: The term to be integrated is x31+x4x^3\sqrt{1+x^4}.; The substitution variable is w=1+x4w = 1+x^4.; The differential dwdw is proportional to x3dxx^3 dx.

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To set up the definite integral for the arc length of the curve y=x3/2y = x^{3/2} over the interval [0,32/9][0, 32/9], you first apply the power rule to find the derivative of the function, which is f′(x)=32x1/2f'(x) = \frac{3}{2}x^{1/2}. Next, you square this derivative to get (f′(x))2=94x(f'(x))^2 = \frac{9}{4}x.

Conditions: The curve is defined by the function f(x)=x3/2f(x) = x^{3/2}.; The interval of integration is [0,32/9][0, 32/9].; The arc length formula ∫ab1+(f′(x))2dx\int_{a}^{b} \sqrt{1 + (f'(x))^2} dx is applicable.

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When using u-substitution in a definite integral, the original limits of integration in terms of xx must be converted into new limits in terms of uu. This is done by substituting the original xx-bounds into the substitution equation u(x)u(x).

Conditions: The integral is a definite integral.; A substitution u=u(x)u = u(x) is being used.; The original limits of integration are given in terms of xx.