## hiralpatel121 2 years ago Can someone help me solve this calc problem? It's attached.

1. hiralpatel121

2. hiralpatel121

Sample problem:

3. myko

you have the solution with the explanation, so what else do you need?

4. hiralpatel121

I have a sample problem. I've tried applying the steps to the actual problem but it's confusing.

5. coreylvaughn

So instead of substituting 6 and 1 into the v's, you'll substitute 5 and 2.

6. coreylvaughn

The substitution takes place at the part where the expression is in square brackets. [ ]

7. coreylvaughn

You'll plug in 5 first and evaluate. Keep that answer on the side somewhere. Then you'll go back to the square brackets again, plug in 2 and evaluate. Whatever you get as the answer, you'll subtract that from the answer you got when you plugged in 5.

8. hiralpatel121

Can you wait while I do it, and tell me if it's correct?

9. coreylvaughn

Yes.

10. hiralpatel121

I got 77.5 when I plugged in 5.

11. coreylvaughn

I got -7.5

12. coreylvaughn

There's an extra negative sign next to the red negative sign. Ignore the extra one.

13. coreylvaughn

${-3(5)^{2}\over 2}+6(5)$

14. hiralpatel121

Okay, so if I plug in 1, I'll get -3/2+8 = 6.5

15. coreylvaughn

No. 4.5.

16. coreylvaughn

Look at the equation I wrote above.

17. coreylvaughn

What do you get when you evaluate that expression?

18. hiralpatel121

Oh, I forgot to square it.

19. hiralpatel121

Then I get: (-7.5+4.5) - (-3/2 +8) = -9.5 or -19/2.

20. coreylvaughn

It's cool.

21. hiralpatel121

It's not correct though.

22. coreylvaughn

You're doing more than what it's asking for. The only values you're evaluating are 5 and 2. Not 6 and 1.

23. coreylvaughn

6 and 1 are solely used in the example.

24. coreylvaughn

You never answered my question. What do you get when you evaluate the expression I wrote above?

25. hiralpatel121

-7.5

26. coreylvaughn

Awesome. Now imagine the 5 is gone and a 2 is in its place in the expression above. What do you get now?

27. coreylvaughn

Replace BOTH 5s with 2s. Not just the one on the left.

28. hiralpatel121

6

29. coreylvaughn

Perfect. Now the last step is subtracting that 6 from -7.5: -7.5 - 6 =

30. hiralpatel121

-13.5

31. coreylvaughn

Awesome : )

32. hiralpatel121

But if you look at the sample problem, they subtracted another part too.

33. coreylvaughn

They subtracted the value of the expression when a 1 was plugged in. We subtracted the value of the expression when a 2 was plugged in.

34. hiralpatel121

I got -8 and it's still wrong.

35. coreylvaughn

-8 on which problem?

36. coreylvaughn

Ugh. It's + 8 not +6

37. coreylvaughn

${-3v ^{2} \over 2}+8v$

38. coreylvaughn

39. hiralpatel121

Okay

40. coreylvaughn

Sorry. I thought the expressions were the same in the example and actual problems.

41. hiralpatel121

It's okay. Can you help with another problem?

42. hiralpatel121

If you're not busy?

43. coreylvaughn

Sure.

44. hiralpatel121

45. hiralpatel121

Sample:

46. coreylvaughn

4/3

47. coreylvaughn

Start off exactly as the example starts by dividing u and -4 by the square root of u. This gives you: $\int\limits_{1}^{9}u ^{1/2}-4u ^{-1/2}$

48. coreylvaughn

Then integrate each term.

49. coreylvaughn

$[{2 \over 3}u ^{3/2}-8u ^{1/2}]$

50. coreylvaughn

Plug in 9 first, and evaluate. Plug in 1 afterwards, then evaluate. Subtract the second answer from the first one.

51. coreylvaughn

Take care and don't forget to mark a Best Response. Thank you