Parabola equation, given the vertex and a point on the curve

[yoda]

vertex at (h, k) = (0, 4)
point on the parabole: (x, y) = (-4, 60)

To solve, I used y = a(x - h)^2 + k where y and x correspond to the point and h and k correspond to the vertex. I put the numbers in:

. . .-60 = a(-4 - 0)^2 + 4

I ended up with a = -3 and the equasion of:

. . .y = -3x^2 + 4

But when I checked my answer, it said the equation was supposed to be:

. . .y = 4x^2 + 4

Nobody I asked could tell me what I did wrong. Did I get the right answer, or did I just mess up?

 

[stapel]

Nobody I asked could tell me what I did wrong.

Until you show your steps, I'm afraid we won't be able to, either. Sorry.

Eliz.

 

[yoda]

I think I might have figured it out. Plugging in h, k, x, and y, I get:

. . .-60 = a(-4 - 0)^2 + 4

. . .-60 = a(16) + 4

Subtract 4 from both sides:

. . .-64 = 16a

Then divide through by 16 to get:

. . .a = -4

=)

 

[stapel]

You listed the point on the curve as being (x, y) = (-4, 60), but you've twice now plugged in (x, y) = (-4, -60). Is the 60 positive or negative? If negative, then you have the correct value for "a".

Eliz.

 

[yoda]

oops thats my bad. it is a -60... thanks for catching that.