Christos 2 years ago Whats the integral of ln(x^2) ?

1. zzr0ck3r

ln(x^2) = 2ln(x)

2. zzr0ck3r

what is the integral of ln(x)?

3. Christos

1/x ?

4. zzr0ck3r

no that's the derivative

5. Christos

wait

6. zzr0ck3r

hint: let u = ln(x) and let dv = 1 dx

7. zzr0ck3r

try not to just give answers? we can go to wolfram for that

8. primeralph

@zzr0ck3r still not the final answer; but I'll take it off

9. Christos

xln(x) ? I still refuse to go by the answer :D

10. primeralph

@Christos xlnx is not the answer. Use integration by parts

11. Christos

xln(x)-1

12. zzr0ck3r

if you are just guessing you can go to wolframalpha and get the answer

13. Christos

I am not guessing I though x has a power of 1 so -1 at the end and outside of ln whatever is inside

14. Christos

I saw it somewhere long time ago but im not sure if its correct

15. zzr0ck3r

u need to do integration by parts

16. zzr0ck3r

is that what you are doing in class?

17. Christos

What is this, can you give me an example?

18. Christos

I am learning alone.

19. zzr0ck3r

do you know what the product rule is with derivatives?

20. Christos

I do

21. zzr0ck3r

it is like the inverse of that, it is how we undo that rule.

22. zzr0ck3r

I would google it and read on it, it takes practice

23. Christos

the reverse?

24. zzr0ck3r

sort of

25. zzr0ck3r

do you know u substitution for integration?

26. Christos

yes

27. zzr0ck3r

ok that "undoes" the chain rule, so now you need to learn by parts. there are both crucial to learning integration http://tutorial.math.lamar.edu/Classes/CalcII/IntegrationByParts.aspx

28. Christos

Look at this please: That's specifically what am trying to solve. http://screencast.com/t/0N48E4lhqM9

29. zzr0ck3r

e^(2*lnx) = e^ln(x^2) = x^2 so you need the integral of x^2 not ln(x^2)

30. Christos

I solved it now :D I know how to find this thing very easy (x^3)/3 without any actual formula

31. zzr0ck3r

yeah:)

32. Christos

thanks

33. zzr0ck3r

np