## poopsiedoodle Group Title Can someone help explain how to do quadratic equations with the quadratic formula? I'll give you a problem. See comments. one year ago one year ago

1. poopsiedoodle Group Title

$\huge 0 = -4(-4t^2 -8t -1)$

2. hba Group Title

Well the first step is to compare your equation with the standard form and get a,b and c $\huge\ ax^2+bx+c=0$

3. poopsiedoodle Group Title

So, how would I do that with this one? Multiply the parentheses stuff by -4?

4. hba Group Title

Seeing your question i would suggest you to first divide your whole equation by -4 and then compare

5. poopsiedoodle Group Title

$\Huge 0=-4t^2 -8t-1$

6. hba Group Title

What is a,b and c in this ?

7. poopsiedoodle Group Title

a=-4 b=-8 c=-1

8. hba Group Title

Good,Now you can use the quad formula. $\huge\ x=\frac{ -b \pm \sqrt{b^2-4ac} }{ 2a }$

9. hba Group Title

The other think which you can do with your equation is that you can take -1 common and then compare so everything becomes positive.you can also do it straight away :)

10. poopsiedoodle Group Title

so, t = -8*√64-4*-4 ------------------ 2*-4 ?

11. poopsiedoodle Group Title

which would then be t=-8*(8+4) ----------- -8

12. poopsiedoodle Group Title

am I getting it right?

13. hba Group Title

It should be +- not *

14. poopsiedoodle Group Title

I don't get it... wouldn't you be multiplying -8 and $\pm √64-4*-4$?

15. hba Group Title

t=-8(+-)(8+4) ----------- -8

16. poopsiedoodle Group Title

Now I'm rather confused.

17. hba Group Title

Lemme show you.

18. hba Group Title

I appreciate you working with me though.

19. poopsiedoodle Group Title

I guess I could do that $$\Huge\mathsf{:P}$$

20. hba Group Title

a=-4 b=-8 c=-1 $\huge\ t=\frac{ -(-8) \pm \sqrt{(-8)^2-4(-4)(-1)} }{ 2(-4) }$

21. poopsiedoodle Group Title

Ok, but what does the $\pm$ do? what's its significance?

22. hba Group Title

Well when we simplify it we would be taking the adding part on one side and subracting part on the other side.

23. poopsiedoodle Group Title

so it'd be 8+√blahblahblah --------------- 2-(-4)?

24. hba Group Title

Either, 8+√blahblahblah --------------- 2-(-4)? Or, 8-√blahblahblah --------------- 2-(-4)?

25. poopsiedoodle Group Title

so the $\pm$ just breaks up between the denominator and the numerator?

26. hba Group Title

Exactly.

27. poopsiedoodle Group Title

Ah. I guess I'll try another problem here and ask you if it's right or something.

28. hba Group Title

Sure :)

29. poopsiedoodle Group Title

$\huge 0=-2x ^{2} +14x +20$ $\large x=\frac{ -14\pm \sqrt{14^2 - 4(-2+20)} }{ -4 }$ $\large x= \frac{ -14+14-72 }{ -4 }$

30. poopsiedoodle Group Title

and the answer is $\huge \frac{ -7\pm \sqrt{89} }{ 2 }$. Would I be right?

31. hba Group Title

Its is -4(a)(c) not -4(a+c)

32. poopsiedoodle Group Title

oh. Well that ruins that then.

33. hba Group Title

Yes it does :) Do it on a paper and tell me what you got from that equation :)

34. poopsiedoodle Group Title

$\Large x=\frac{ -14\pm \sqrt{14^2 - 4(-2*20)} }{ -4 }$ $\Large x=\frac{ -14\pm 14 - 4(-40)} { -4 }$ $\Large x=\frac{ -14\pm 14-160} { -4}$ $\Large x=\frac{ -14\pm -146} {-4}$ set x to 0 and divide all by -2 to get $\Large \frac{ 7\pm 73} { 2}$

35. poopsiedoodle Group Title

and now I'm confused.

36. poopsiedoodle Group Title

oh wait, I forgot to keep the x's in there. Crap.

37. poopsiedoodle Group Title

Think you could help me out here? My mind is about to implode.

38. hba Group Title

x=7+73/2,x=7-73/2

39. hba Group Title

Btw, (-) *(-)=+

40. hba Group Title

So just because of signs it goes wrong.

41. hba Group Title

$\Large x=\frac{ -14\pm 14 - 4(-40)} { -4 }$ Continue from here.

42. poopsiedoodle Group Title

But I left the xs out of my work. ._.

43. hba Group Title

44. hba Group Title

Continue working from here.

45. poopsiedoodle Group Title

$\Large x=\frac{ -14\pm 14 - 4(-40)} { -4 }$ $\Large x=\frac{ -14\pm 14+160} {-4}$ $\Large x=\frac{ -14\pm 174} {-4}$ $\Large x=\frac {\frac{ -14\pm 174} {-4}} {-2}$ $\Large x=\frac {7\pm -87} {2}$

46. poopsiedoodle Group Title

And now what do I do?

47. hba Group Title

I don't know what you are upto ,where did that divide by -2 come in between ?

48. poopsiedoodle Group Title

Well, I'm not sure. I just thought I had to do that. I'm rather confused ._.

49. hba Group Title

Hmm,If OS would be working on chrome i would have worked one problem for you. Can we do this later ?

50. poopsiedoodle Group Title

I'm using chrome right now o_o But, I guess that'd be OK :P

51. hba Group Title

Thanks.

52. poopsiedoodle Group Title

Thanks to you too :3