A equation that im stuck on

1. Feb 12, 2007

thomas49th

1. The problem statement, all variables and given/known data

2. Relevant equations

As in the image above

3. The attempt at a solution

I had a go but i rubbed it off the sheet.

Can someone take me through this step by step on how to solve it

Thanks

2. Feb 12, 2007

HallsofIvy

Staff Emeritus
What is your question? You are told exactly what to do!

You are told that the equation must be of the form
S= at2+ bt+ c.

You are given t and S values for 6 different values of t.
Putting the given x and t values into the equation above for 3 different values of t (t= 0, 2, 3, as they suggest, will do but the choice is yours) will give you 3 equations to solve for a, b, and c. (Taking t= 0 will get an especially easy equation!)

3. Feb 12, 2007

thomas49th

so

t=0: 0 = 0 + 0 + 0 (c will have to be 0 if a and b are)
t=1: 10 =a+b+c
t=2: 30 =4a+2b+c
is that right?

Last edited: Feb 12, 2007
4. Feb 12, 2007

jing

but where does it say a and b are 0?

t=0: 0 = a.0 + b.0 +c and hence c=0

the other equations are correct

5. Feb 12, 2007

thomas49th

if t = 0
then a x t = 0
b x t = 0
so c must be 0 if the equation equals 0

6. Feb 12, 2007

jing

Correct. Now use that you know c=0 in the other two equations

7. Feb 12, 2007

thomas49th

Huh? I thought the other 2 equations were right?

t=0: 0 = 0a + 0b + 0
t=1: 10 =a+b+c
t=2: 30 =4a+2b+c

cant I right them as that?

8. Feb 12, 2007

jing

Yes they are correct but you now know that c = 0

so a+b+c=a+b

and

4a+2b+c=4a + 2b