MATH HELP! For people who love math?

Question

Applications The formula h = -16t 2 + 212 gives the distance a bungee jumper is from the ground for the free-fall portion of the jump, t seconds after leaping off a bridge. We can find the number of seconds it takes the jumper to reach the point in the fall where the 64-foot bungee cord starts to stretch by substituting 148 for h and solving for t. Find t.
My answer was t = 4 however it was wrong heres my work.

148=-16t^2+212
standard form
16t^2-64=0
16(t^2-4)=0
16t=0 t-4=4

answer 4 seconds. I basically followed the example in the book.

second question

Practice Solve the equation.
3z3 - 432z = 0
there should be 3 answers

i only got one correct answer 0
the other two i got were wrong but they were -216 and 72


please help and PLEASE show your work.

oh i almost forgot this one to

Practice Solve the equation.
2x^2 - 9x = -10

i used the quadradic formula and got 2 & -2.5 but thats not right UGH

you all are the best. I wish I could choose all three of you as the best answer. But i cant. so what i did was i looked at the person with the least amount of "best answers" then since it was a tie looked at the person who had the least level points. I hope i was fair. But I thank you all.... now i only have 67 problems or so to worry about. THANKS!

ok a few more.. i am really stuck on these

Answer 1

On the bungee question, you were doing great up until the end.

16(t^2-4)=0 is right. Divide by 16 to get
t^2-4=0

This factors as (t-2)(t+2)=0, so t=2 or t=-2.



For the cubic equation
3z^3 - 432z = 0, I'd divide by 3:
z^3 - 144z = 0. Now factor out z:
z(z^2-144) = 0. Here we see another difference of two squares (like the previous problem), so we can factor it:
z(z-12)(z+12)=0. This tells us z=0, 12, or -12.



On the last one, I think you did the quadratic formula *mostly* the right way; it's just that both answers should be positive.

2x^2 - 9x = -10 should be rearranged as
2x^2 - 9x +10 = 0.

Now factor it as (2x-5)(x-2) = 0 (and the rest pops out quickly) or apply the QF:

x = [9 +- Sqrt(81-80)] / 4
= [9 +- 1] / 4
= 10/4, 8/4
= 2.5, 2

Answer 2

you were almost there on number one, you just left the squared part off of t:

it should be

16(t^2 - 4) = 0 so t^2 - 4 = 0 so t^2 = 4 or t=2

#2.

3z^3 - 432z = 0
3z(z^2 - 144) = 0

so

3z = 0 so z=0 and
z^2 - 144 = 0 so z^2 = 144 so z = +12 and z = -12

i don't know where you are getting -216 and 72 from

#3. i don't think you have to use the quadratic formula

2x^2 - 9x = -10
2x^2 - 9x + 10 = 0
factoring gives you
(2x - 5)(x - 2) = 0 so

2x - 5 = 0 x=5/2 and x - 2 = 0 so x = 2

hope this helps you out a little

Answer 3

148 = -16t^2 +212
148-212= -16t^2
-64 = -16t^2
-64/-16 = -16t^2/-16
4=t^2
2=t

This may be right...I think you just forgot to take the square root...hope that helps