# evaluating a parabola in equation form.

• Jan 20th 2011, 10:55 AM
quikwerk
evaluating a parabola in equation form.
I don't really understand how to do this question:

If parabola \$\displaystyle 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, 10:57 AM
e^(i*pi)
Can't you simply sub in (2,0) for (x,y)?

\$\displaystyle 0-2 = a(2-3)^2\$
• Jan 20th 2011, 11:21 AM
quikwerk
So I was overthinking it?
I see, so 'a' is -2?
• Jan 20th 2011, 11:23 AM
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, 11:47 AM
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!