## sat_chen 2 years ago integral subsitution confused

1. sat_chen

|dw:1359530329483:dw|

2. sat_chen

|dw:1359530356277:dw|

3. sat_chen

|dw:1359530523166:dw|

4. sat_chen

what the heck do you do after this

5. dumbcow

are those 9's inside radical ?

6. sat_chen

you dont have to write the whole steps like last time can you just give me advice and yes they are

7. sat_chen

and you can just make them easy by making them into (3/7x)^2

8. sat_chen

|dw:1359530730683:dw| (3/7x)^2 something like that for the bottom part

9. sat_chen

when you do it can you confirm that you get the same solution as in my solving part and help me from there on. thanks

10. dumbcow

ok i get same solution (i simplified the constants) $\frac{343}{81}(\frac{\sec^{3} \theta}{3} - \sec \theta) +C$ now you have to substitute back in "x" $\tan \theta = \frac{3x}{7}$ and $\sec^{2} \theta = \tan^{2} +1 = \frac{9x^{2}}{49} +1 = \frac{9x^{2} +49}{49}$ take sqrt to get "sec" , then cube that to get sec^3

11. sat_chen

so you wouldd ger 3x +7 /7 ?

12. sat_chen

for sec

13. dumbcow

no it would be ... sqrt(9x^2 +49) /7 because of addition inside you can't just take sqrt of each term

14. sat_chen

oh right right silly me

15. sat_chen

|dw:1359532127694:dw|

16. sat_chen

is that it?

17. dumbcow

yep ... oh dont forget the 3 in denominator probably need to s.continue to simplify

18. sat_chen

but hold on my angles look like this |dw:1359532285169:dw|

19. dumbcow

hmm hypotenuse should be .... sqrt(9x^2 +49)

20. sat_chen

oh f i see why i forgot to square. its 2am and i had a long day -.-

21. dumbcow

haha time to get some sleep ....have wolfram do work for you

22. sat_chen

yep just finished it got the right answer thanks a lot time for bed i cant even think straight right now

23. sat_chen

u in us too?

24. dumbcow

yeah about 1 am here in AZ (best state)

25. sat_chen

and dont use wolfram like to get these things down myself

26. sat_chen

u in college?

27. sat_chen

taking engineering math not my strongest subject but where the jobs go i go XD

28. dumbcow

nope... finished with college , i work as a math tutor so i come on here to practice and help people

29. sat_chen

hmm so you planning to be a teacher you would be a good one

30. dumbcow

engineering is great field but tough classes have to take quite a bit of math

31. sat_chen

yep still got to diff linear algebra etc good night bed is calling for me :P

32. dumbcow

i qualified to be a teacher but am undecided .... i prefer tutoring 1 on 1 ..... classroom teaching isn't my style

33. dumbcow

bye

34. sat_chen

you would be a great 1 v1 tutor too yea good night