Skip to content
START WITH A QUESTION

What would you like to understand?

Find an answer. See the moment it becomes clear. Follow the idea further.

← Concept directory

Answers for “如何计算定积分 \frac{4}{9}\int_{1}^{9}\sqrt{u}\,du?”

3 keyword matches

Understanding your question. You can explore the search results below now.

Meet the concept

↗

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.

Find a method

↗

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.

Understand why

↗

The substitution u=1+94xu = 1 + \frac{9}{4}x is chosen because it is exactly the expression under the radical in the arc-length integral ∫032/91+94x dx\int_0^{32/9}\sqrt{1+\frac{9}{4}x}\,dx. By setting uu to this inner expression, the complicated integrand simplifies to u\sqrt{u}, which is much easier to integrate using the power rule.

Conditions: The integral to evaluate is ∫032/91+94x dx\int_0^{32/9}\sqrt{1+\frac{9}{4}x}\,dx.; The integrand contains a composite expression under a square root.