## anonymous 3 years ago mathcalculus HELP: Determine the values of where the tangent line is horizontal for the function:

1. anonymous

2. anonymous

i know i have to find the derivative and set it to zero but it's not coming out to be correct. can anyone help me

3. anonymous

so i did 3x^2-6x-4=0

4. anonymous

i tried to use the quadratic formula and got sqrt(21)+3/3

5. anonymous

+ or - sqrt(21)+3/3

6. anonymous

also aka 2.52753...

7. anonymous

derivative seems correct

8. anonymous

to find what x = to... ?

9. anonymous

10. anonymous

@dumbcow dont i have to do that to find x??

11. anonymous

im getting it wrong,

12. anonymous

yes everything looks correct to me...do they want exact or decimal answer?

13. anonymous
14. anonymous

can i use quadratic formula for ths one?

15. anonymous

@dumbcow

16. anonymous

??

17. anonymous

????????????????????????

18. anonymous

yes of course you use quadratic formula...thats how you got your answer that i said looked correct

19. anonymous

im not getting that using quadratic formula

20. anonymous

im getting something totally different and wrong

21. anonymous

$x = \frac{3 \pm \sqrt{21}}{3}$

22. anonymous

yes! but from 6+2*sqrt(21)/6?

23. anonymous

shouldnt it be 1+ or - sqrt 21/3

24. anonymous

same thing, just a matter of splitting up fraction or keeping it as single fraction

25. anonymous

no it's not because the answer is 1+ sqrt (7/3) gives me 2.52753 and 1+sqrt 21/3 gives me 1.86086!

26. anonymous

@dumbcow

27. anonymous

hmm $\frac{\sqrt{7}}{\sqrt{3}} = \frac{\sqrt{21}}{3}$

28. anonymous

hmmm?

29. anonymous

@dumbcow

30. anonymous

try it on a calculator.

31. anonymous
32. anonymous

oh you added the "1" before dividing by "3"

33. anonymous

okay from my answer.... not the internet.. 6+2 sort(21)/3.... where do i go from there?

34. anonymous

well it should be a 6 on bottom

35. anonymous

36. anonymous

okay sure a 6. i thought it could be a 3 to narrow it down

37. anonymous

so 6+or-2sqrt(21)/6

38. anonymous

i dont see the problem, you posted answer in beginning... " i tried to use the quadratic formula and got sqrt(21)+3/3 "

39. anonymous

so it is a 3 in the denominator!

40. anonymous

$\frac{6 \pm 2\sqrt{21}}{6} = \frac{2(3 \pm \sqrt{21})}{6} = \frac{3 \pm \sqrt{21}}{3}$