## Shido88 2 years ago Find the Vertex: f(x)= -3x^2-7x+6

1. Shido88

@saifoo.khan helpppp lol

2. saifoo.khan

Hey. To find vertex there's a shortcut.

3. Shido88

uh huh

4. saifoo.khan

to find the x-cordinate, use this formula: -b/2a

5. saifoo.khan

-(-7)/2(-3)

6. Shido88

that will give me the vertex ?

7. saifoo.khan

Yes. "x-cordinate" of vertex.

8. saifoo.khan

Solve it first..

9. Shido88

kk hold on :)

10. saifoo.khan

Holding.. :)

11. Shido88

got 7/6

12. Shido88

vertex is (h,k) right? so i believe that is the "h" ?

13. saifoo.khan

Perfect. ^

14. saifoo.khan

Find k now.

15. Shido88

how to find k lol ?

16. saifoo.khan

17. Shido88

i got it lmao :))

18. Shido88

hold on

19. saifoo.khan

Okay. so now use 7/6 to find it. y = -3x^2-7x+6 y = -3(7/6)^2 -7(7/6) + 6 solve.

20. Shido88

got decimal :( hate decimal

21. Shido88

so the vertex would be : (7/6, -6.24) ?

22. saifoo.khan

Should be 121/12

23. Shido88

wtf ?

24. Shido88

how? :O

25. Shido88

-156/25

26. Shido88

hey come back here >:o

27. saifoo.khan

VERTEX SHOULD BE -7/6. -_-

28. saifoo.khan

THE X-CORDINATE.

29. Shido88

CALM DOWN !! CAPS WAR XD

30. saifoo.khan

ONE NEGATIVE SIGN RUINS EVERYTHING. >_<

31. Shido88

so -7/6 because its opposite of 7/6 ?

32. Shido88

you suppose to change it everytime ?

33. Shido88

how come my teacher didn't change it -_____-

34. saifoo.khan

No. we calculated the x-cordinate wrong in the first place.

35. Shido88

oh....XD

36. saifoo.khan

$-\frac{b}{2a} \to -\frac{(-7)}{2(-3)}\to \frac{7}{-6} \to -\frac 76$

37. Shido88

ohhhhhhhhh i see now lmao hhahaha :D

38. Shido88

omfg...my whole problem is wrong, thanks saif ! lol : XD

39. Shido88

+99 medals

40. saifoo.khan

;D Thanks.

41. Shido88

hmm instead of 121/10 should i just leave it as 10.08 cuz i have to graph this afterward ?

42. Shido88

great now i gotta calculate x-int and y-int :| let see......

43. saifoo.khan

Sure. Same thing. Depends on in what format your teacher wants

44. Shido88

stay there.. lol

45. saifoo.khan

Lol. okays.

46. Shido88

stuck lol....find x-intercept?

47. Shido88

i know let y=0

48. Shido88

0=-3x^2-7x+6

49. Shido88

-6=-3x^2-7x <-----stuck here..

50. saifoo.khan

51. Shido88

oh yee

52. saifoo.khan
53. Shido88

but the way my teacher did it was to set y=0 and just add and divide stuff on left and right side...which is confusing but i suppose we can use quadratic aswell :)

54. saifoo.khan

Your teacher must have used the "completing the square" method. It's hella confusing. It confuses me too. :/

55. Shido88

yeah thats what that was, completing the square lol.... ok i got y= 7+- sqrt(-23)/-6 and what's next ?

56. Shido88

i dont think u can reduce it down or anything right? and u can't even square root a negative

57. saifoo.khan
58. saifoo.khan

No. We can't reduce.

59. saifoo.khan

u can't even square root a negative Yes you're very right.

60. Shido88

ohh i get it, it's 7+- 23i/-6

61. saifoo.khan

Roots are: -14 and 0.

62. saifoo.khan

Roots are: -3 and 2/3

63. Shido88

what? @_@

64. Shido88