What is the integral int (x^2+1)(x^3+3x)^4 dx?
`int (x^2+1)(x^3+3x)^4 dx`
Use U-substitution to solve this.
Take the derivative. Notice that there is a common factor of three!
`dU= 3x^2 +3 dx= 3(x^2+1) dx`
Divide by three on both sides, and then we will see that we can plug in `(x^2+1) dx`
`1/3 dU = (x^2+1) dx`
Now that we know and , substitute these back to the integral.
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