## anonymous 4 years ago integrate x^3.logx

1. anonymous

limits?

2. anonymous

hw do u decide the functions f and g

3. anonymous

no it is indefinite integral

4. anonymous

i have been told a order for that

5. anonymous

guess what? parts again

6. anonymous

ya......u gotta explain me d best fit technique

7. anonymous

well this time it will be easier to find the anti derivative of $x^3$ then to keep integrating $\ln(x)$so i would make $u=\ln(x), du =\frac{1}{x}dx, dv = x^4, v=\frac{x^4}{4}$ and it should work out nicelyi

8. anonymous

notice that in the first step the log is gone, and you can simplify the second integral easily because you will end up with $-\frac{1}{4}\int \frac{x^4}{x}dx=-\frac{1}{4}\int x^3dx$ so you will be done after one step

9. anonymous

got it ..this needs practice i guess

10. anonymous

that is the only way you will know what to pick. on the other hand, if you picked $dv=\ln(x)$ then you would have $v=x\ln(x)-x$ and you see that your second integral would be a real pain

11. anonymous

ya tryed it that way it was hard