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Answers for “为什么在这个演示示例中 9^{3/2}-1^{3/2} 变成 26?”

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Understand why

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The expression 93/2−13/29^{3/2}-1^{3/2} becomes 26 because 93/29^{3/2} evaluates to 27 and 13/21^{3/2} evaluates to 1. The power 93/29^{3/2} can be calculated by taking the square root of 9, which is 3, and then cubing it, resulting in 33=273^3 = 27.

Conditions: The expression is evaluated exactly using integer powers.; 93/2=279^{3/2} = 27 and 13/2=11^{3/2} = 1.

Meet the concept

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The antiderivative of u\sqrt{u} is found by rewriting the square root as a fractional power, u1/2u^{1/2}, and then applying the power rule for integration. The power rule states that ∫undu=un+1n+1\int u^n du = \frac{u^{n+1}}{n+1}.

Conditions: The integrand is u\sqrt{u}, which is equivalent to u1/2u^{1/2}.; The power rule for integration is applicable.; u≥0u \ge 0 for the real-valued square root form.

Understand why

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The presenter factors out the common coefficient 23\frac{2}{3} to make the subsequent arithmetic simplification easier. After evaluating the antiderivative at the upper and lower bounds, both terms inside the brackets contain the factor 23\frac{2}{3}.

Conditions: The expression to evaluate is 49[23⋅93/2−23⋅13/2]\frac{4}{9}\left[\frac{2}{3}\cdot 9^{3/2}-\frac{2}{3}\cdot 1^{3/2}\right].; Both bracketed terms contain the same factor 23\frac{2}{3}.