AP Calculus AB / Unit 6: Integration and Accumulation of Change
6.9 Integrating Using Substitution
Notes
Use $u$-substitution when you see a function and its derivative (up to a constant):
- Let $u$ be the inside function; find $du$.
- For definite integrals, change the limits to $u$-values (or switch back to $x$).
Practice
$\displaystyle \int 2x(x^2+1)^5\,dx=$
$u=x^2+1$, $du=2x\,dx$.
$\displaystyle \int\cos(3x)\,dx=$
$u=3x$, $\displaystyle dx=\frac{du}{3}$.
With $u=x^2$, the integral $\displaystyle \int_0^2 x e^{x^2}dx$ has new limits:
$u(0)=0$, $u(2)=4$.
Ready for more? Take the Unit 6 test.