How to integrate with given substitution?

38 Views Asked by At

Using the substitution $u = x^2e^{-4x} + 3$, find $$\int\frac{x(1-2x)}{x^2+3e^{4x}} dx$$

1

There are 1 best solutions below

0
On BEST ANSWER

Observe that $$I\stackrel{\text{def}}{=}\int\frac{x(1-2x)}{x^2+3e^{4x}}\:dx=\int\frac{xe^{-4x}(1-2x)}{x^2e^{-4x}+3}\:dx=\int\frac{du}{2u}=\frac{1}{2}\ln{|u|}+C$$ where $u = x^2e^{-4x}+3$.