# evaluating a parabola in equation form.

• Jan 20th 2011, 11:55 AM
quikwerk
evaluating a parabola in equation form.
I don't really understand how to do this question:

If parabola $y-2=a(x-3)^2$ goes through the point (2,0), what is the value of a?

I have been able to determine that its vertex is (3,2) meaning that 'a' must be negative.
However, I have no idea about how to derive a number....

• Jan 20th 2011, 11:57 AM
e^(i*pi)
Can't you simply sub in (2,0) for (x,y)?

$0-2 = a(2-3)^2$
• Jan 20th 2011, 12:21 PM
quikwerk
So I was overthinking it?
I see, so 'a' is -2?
• Jan 20th 2011, 12:23 PM
e^(i*pi)
Yes, and it fits in with your working that it must be negative.

You were told that the equation passes through that point so that point must be a solution for the equations. I thought it would be more complicated at first
• Jan 20th 2011, 12:47 PM
quikwerk
Quote:

Originally Posted by e^(i*pi)
Yes, and it fits in with your working that it must be negative.

You were told that the equation passes through that point so that point must be a solution for the equations. I thought it would be more complicated at first

Ah, I feel quite dim....
But I have learnt something, so its not so bad!

Thank you very much for your help!