College Algebra

A quadratic function has its vertex at the point (-9,8). The function passes through the point (9,4). When written in vertex form, the function is f(x)= a(x-h)^2 +k, where

a)
h)-9
k)8

4=a(9)^2+8
4=a(9+9)^2+8
4=a(18)^2+8
4=a(332)
a=0.01204

I was able to find both h & k. but the answer I got for a is incorrect, please help me

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  1. from vertex,
    y = a(x+9)^2 + 8
    but (9,4) lies on it, so

    4 = a(18^2) + 8
    324a = -4
    a = -4/324 = -1/81
    etc

    you messed up here:
    4=a(18)^2+8
    4=a(332) , you added 8 to 324a , you can't add unlike terms

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    posted by Reiny

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