## ta123 4 years ago need help on the attachment @Calculus1

1. ta123

2. ta123

hey you know on the other problem you were helping me with lagrange?

3. ta123

what did you get for the answer because I got -4 and they counted it wrong

4. LagrangeSon678

i got 2

5. LagrangeSon678

are u sure you evaluated correctly

6. ta123

oh, made a stupid sign error

7. ta123

could you help me with this new problem on the attachment

8. LagrangeSon678

yeah let me look at it

9. LagrangeSon678

okay so this is what you wanna do, set u=x+4, then you have to then rewrite x in terms of u. You can do this simply by saying x=u-4

10. ta123

ok

11. LagrangeSon678

|dw:1321490017407:dw|

12. LagrangeSon678

|dw:1321490044699:dw|

13. LagrangeSon678

|dw:1321490067161:dw|

14. ta123

do you replug the original function into u after integrating

15. LagrangeSon678

yes after you, integrate, you must replace the orginal function

16. ta123

did you get u^2/2-3x*2U^(1/2) after integrating

17. LagrangeSon678

give me a sec

18. LagrangeSon678

i led you wrong, my mistake. What you want to do, is let u=sqrt(x+4), now we rewrite x interm of u. To do this simply:|dw:1321490856188:dw|

19. LagrangeSon678

okay, now you should get:|dw:1321490948435:dw|

20. LagrangeSon678

now let fix up that integral:|dw:1321491019469:dw|

21. LagrangeSon678

|dw:1321491091199:dw|

22. LagrangeSon678

now recall that u=sqrt(x+4), thus we can divide out the u in the denmominator and the sqrt(x+4) as so:|dw:1321491198348:dw| The two can be put outside the integral since it is a constant

23. LagrangeSon678

now simply we have:|dw:1321491263984:dw|

24. LagrangeSon678

next you have to integrate that, and then replace the u's. Then evaluate over your limits

25. LagrangeSon678

or, we could simply change the limits interms of u. Which would actaully be much eaier in this case. But i leave that up to you to decide on

26. ta123

sqrt(x+4) did both cancel out and when you replace the u on the bottom back to x+4 don't you have to do the same thing to the top?

27. LagrangeSon678

on top we had u^2-3, cause we replaced the x remeber

28. ta123

oh, ok also you forgot to label the endpoints on the integral

29. LagrangeSon678

well,i didnt forget, for me it is simpler to first leave the limits while i do the integration, since they really dont matter untill we get the antiderivative, which we then evlauate over the limits

30. ta123

I got -44

31. ta123

is that right?

32. ta123

???

33. LagrangeSon678

yes i did,1 is the correct answer

34. ta123

Thanks could you help me with one more of these problem?

35. LagrangeSon678

sure

36. LagrangeSon678

37. ta123

38. LagrangeSon678

i cant open it

39. ta123

40. ta123

could you open it?

41. LagrangeSon678

yeah, okay lets do this, can we multiply the x into the brackets, then seperate the integral into two spereate integrals:|dw:1321500013159:dw|

42. LagrangeSon678

now lets take out some constants: |dw:1321500075388:dw|

43. LagrangeSon678

now let try this, can we for the first integral, let x^2=u, then du=2xdx, which further means du/2x=dx

44. LagrangeSon678

now it should look something like this:|dw:1321500219046:dw|

45. LagrangeSon678

now we see that the x will divide out, and the 1/2 from the du can be taken outside the integral, so now we will get :|dw:1321500319063:dw|

46. LagrangeSon678

now 2*1/2 is simply 1, so we now have:|dw:1321500384165:dw|

47. LagrangeSon678

now we can integrate

48. LagrangeSon678

for the first integral, what i the antiderivative of f'? well its simply f, the orginal function , and the second integral is very simpyle to integrate

49. LagrangeSon678

|dw:1321500486597:dw|

50. LagrangeSon678

|dw:1321500522223:dw|

51. LagrangeSon678

but lets replace the u:|dw:1321500561883:dw|

52. LagrangeSon678

now you can evaluate this over you limits but remeber that you were given certain conditions, namely f(1)=3 and f(0)=1.so we have|dw:1321500688385:dw|

53. LagrangeSon678

furthermore:|dw:1321500784828:dw|

54. LagrangeSon678

Got it

55. ta123

yes, I was just was reviewing all the work, thanks!

56. LagrangeSon678

anytime:)soon you will be an expert on calculus and you will be helping others as well

57. ta123

I hope so, thanks again

58. LagrangeSon678