## anonymous 4 years ago im lost ... −16t2+80x−60=0 Solving for t, t=(5±10−−√)2

1. lgbasallote

why do you have mixed variables -__-

2. campbell_st

well simplify the problem -4(4t^2 - 20t +15)

3. anonymous

Ah this is the a nswer i gave you earlier for the height?

4. anonymous

yeah im lost

5. campbell_st

so using the GQF $t = (20\pm \sqrt{(-20)^2-4\times4\times15})/(2 \times4)$ $t = (20 \pm \sqrt{16 \times10})/8 = (5\pm \sqrt{10})/2$

6. anonymous

7. anonymous

Screw it the equation th ing is broken

8. anonymous

Use the quadratic formula to s olve for t

9. anonymous

$t=\frac{-b \pm \sqrt{b^2-4ac}}{2a}$

10. anonymous

I dont think ive learned that yet

11. anonymous

in my class

12. anonymous

Is this a physics problem or calculus?

13. anonymous

calculus

14. anonymous

You should've learned the quadratic formula back in algebra

15. anonymous

woops....

16. anonymous

lol

17. anonymous

so i would just plug in the numbers that were found in the early part of the question?

18. anonymous

$ax^2+bx+c=0$, you can only use the quadratic formula when you have your equation like this

19. anonymous

in this case you do, and you can also divide out a 4 from all the terms 16,80, and 60

20. anonymous

$-4t^2+20x-15=0$ a=-4 b=20 c=-15

21. anonymous

ok? so now I can solve by getting

22. anonymous

by itself

23. anonymous

T

24. anonymous

no, use the quadratic formula as it is written above right now, $t=\frac{-b \pm \sqrt{b^2-4ac}}{2a}$

25. anonymous

$t=\frac{-20 \pm \sqrt{20^2-4(-4)(-15)}}{2(-4)}$

26. anonymous

$t=\frac{-20 \pm \sqrt{160}}{-8}=\frac{-20 \pm 4\sqrt{10}}{-8}=\frac{-5 \pm \sqrt{10}}{-2}=\frac{5 \pm \sqrt{10}}{2}$

27. anonymous

t= -20 sqrt 360/-8

28. anonymous

look above

29. anonymous

wow im way off!!

30. anonymous

Remember to keep the positive and negative signs for a,b,c

31. anonymous

so now I have 3.16227766/2 = 1.58113883

32. anonymous

5+ or - = 1.58113883

33. anonymous

$t \approx .9189s, t \approx 4.081s$

34. anonymous

can you give me the all the numbers shown on your calculator

35. anonymous

They are irrational numbers, there are infinitely many decimal places

36. anonymous

Use the answer with the square root

37. anonymous

That is accurate

38. anonymous

no just the numbers shown on your calculator bcause I need the precise number

39. anonymous

You can't get a precise number from an irrational number! Use $t=\frac{5 \pm \sqrt{10}}{2} s$

40. anonymous

41. anonymous

what I mean is when plug the answers into the my computer it needs the closets thing to an approximate number

42. anonymous

so it must have the all the numbers shown from the calculator for it to be correct

43. anonymous

Your calculator can show hundreds of digits if you want it to

44. anonymous

How many decimal places do you need?

45. anonymous

$t \approx 0.918861169916s, t \approx 4.08113883008s$

46. anonymous

like im using a standard calcultor so it only shows like 9 or 10 numbers

47. anonymous

here are my instructions : For example, the fraction 2/3 is exact, while the decimals 0.67, 0.666666667 and 0.666666666666666666667 are all approximate values for 2/3. Where an exact answer is called for, an approximate answer will be marked wrong.

48. anonymous

So if you use a decimal here, you will be wrong

49. anonymous

yup lol

50. anonymous

Use the answer i gave you with the square root

51. anonymous

so like t t= .9189 just sqrt it

52. anonymous

...

53. anonymous

$t=\frac{5+\sqrt{10}}{2}, t=\frac{5-\sqrt{10}}{2}$

54. anonymous

Those are the exact answers for the time

55. anonymous

ok got it , thanks sorry for the confusion !!