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megpie
09-16-2009, 11:49 PM
I am trying to figure out a very challenging In/Out Table that my teacher gave me today:
IN OUT
0 -
1 -
2 -
3 0
4 2
5 5
6 9
20 ?

I have figured out that delta y / delta x goes up by 1 starting with x=3 y=0. But I cannot figure out a rule. Where do I begin? Thanks

Subhotosh Khan
09-17-2009, 12:05 AM
I am trying to figure out a very challenging In/Out Table that my teacher gave me today:
IN OUT
0 -
1 -
2 -
3 0
4 2
5 5
6 9
20 ?

I have figured out that delta y / delta x goes up by 1 starting with x=3 y=0. But I cannot figure out a rule. Where do I begin? Thanks

Since the difference is going up linearly - this is a quadratic curve.

So fit the equation

y = Ax[sup:368fggt7]2[/sup:368fggt7] + Bx + C

.

mmm4444bot
09-17-2009, 12:31 AM
… Where do I begin? …

That depends upon what algebra you've learned, so far.

Can you solve a system of equations?

If you can, then take any three of the given ordered pairs (x, y) and substitute them one pair at a time into the quadratic equation posted above by Subhotosh.

That will give you three equations containing the parameters A, B, and C.

Solve this system of three equations for the values of A, B, and C.

You'll then have a formula for finding any corresponding y to a given x.

Please show us what you're doing, if you need more help.

Cheers ~ Mark

megpie
09-17-2009, 01:04 AM
thank you for this help but I have'nt done quadratic equations yet.

mmm4444bot
09-17-2009, 01:16 AM
… but I have'nt done quadratic equations yet.

The equations in the system that I described above are all linear.

You don't need experience solving quadratic equations to solve linear equations.

Can you solve the following linear equation for A?

-2A = -1

BTW, you did not answer my direct question.

Can you solve a system of equations?

I could show you an example, but right now we're playing a guessing game with each other.

megpie
09-17-2009, 10:14 AM
Yes, I understand a little bit better..I can solve a system of equations. -2A=-1=1 Thanks!

Subhotosh Khan
09-17-2009, 10:19 AM
Yes, I understand a little bit better..I can solve a system of equations. -2A=-1=1 Thanks!

I am not sure what you are trying to do there!

What level of math are you trying to do? High school Algebra ?? College??

megpie
09-17-2009, 10:58 AM
mmm4444bot asked me if I could solve a system of equations and gave me the example" -2A = -1 oops, I see what I did wrong the first time. the answer is
A= 1/2 right?

I understand better that I should take any pairing in my challenge problem and plug in the x,y into each part of the quadratic equation you gave me. I will try it at school..I have to catch the bus!

i'm in 8th grade doing pre Algebra/Algebra.

Thank you

Subhotosh Khan
09-17-2009, 12:13 PM
These problems can allso by "staring down". If stare with concentration you might find that:

y = x * (x-3)/2 .... (in other words A = 1/2, B = -3/2 and C = 0)

"staring down" does not work always - the "matching coefficient" will always work.