SOLUTION: A function y=ax^2-4x-c. If the y-int is -3 and the co-ordinates of the vertex is (2,-7), find the value of a. Thanks!

Question 1046124: A function y=ax^2-4x-c. If the y-int is -3 and the co-ordinates of the vertex is (2,-7), find the value of a.
Thanks!
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
ax^2-4x-c
Vertex is (h,k) where h=2 and k=-7
This is a(x-h)^2+k
a(x-2)^2-7 is the function, and when x=0, y=-3 (y-intercept)
Therefore a(-2)^2-7= -3
4a-7=-3
4a=4
a=1 ANSWER
Therefore, the function should be (x-2)^2-7 in vertex form or
x^2-4x-3 in standard form.

Another way to check this or to do it is the vertex x component is -b/2a.
We know the vertex is -(-4)/2a=2 (the 2 is given)
4/2a=2
4=4a
a=1
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