SOLUTION: If given a picture of the graph, the vertex of (-1, 5) and another set of points, (2, -13), how do you write the equation in vertex form, f(x) = a(x-h)^2 +k? I know part of the eq

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: If given a picture of the graph, the vertex of (-1, 5) and another set of points, (2, -13), how do you write the equation in vertex form, f(x) = a(x-h)^2 +k? I know part of the eq      Log On


   

Question 266543: If given a picture of the graph, the vertex of (-1, 5) and another set of points, (2, -13), how do you write the equation in vertex form, f(x) = a(x-h)^2 +k? I know part of the equation is f)x) = a(x+1)^2 +5, but how do I find the "a".
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
You are on the right track. We start with
(i) f%28x%29+=+a%28x%2B1%29%5E2+%2B5
we are given the point (2,-13)
put that into (i) and we can see the only variable is "a". We get
(ii) -13+=+a%282%2B1%29%5E2+%2B5
simplify the right to get
(iii) -13+=+9a+%2B+5
subtract to get
(iv) -18+=+9a
divide to get
(v) a+=+-2
so we get our answers as
(vi) f%28x%29+=+-2%28x%2B1%29%5E2+%2B5