Posted by **paige** on Tuesday, October 23, 2012 at 6:59pm.

Write the equation of the quadratic function with roots -2 and 4 and a vertex at (1, 9).

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**Reiny**, Tuesday, October 23, 2012 at 7:07pm
since roots are -2 and 4,

equation must be

y = a(x+2)(x-4)

but (1,9) lies on it, so

9 = a(3)(-3)

a = -1

y = -1(x+2)(x-4)

or

y = -x^2 + 2x + 8

or

y = -(x-1)^2 + 9

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