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April 18, 2014

April 18, 2014

Posted by **Lee** on Monday, October 29, 2012 at 3:54pm.

(-2,-20),(0,-4),(4,-20)

Please Help

- algebra -
**Steve**, Monday, October 29, 2012 at 4:27pmyou can probably save some time by looking at the points. You know that parabolas are symmetric, so, since y(-2) = y(4), the axis of symmetry is at x=(-2+4)/2 = 1.

So, with x=1 the axis of symmetry (and hence at the vertex), you will have

y = a(x-1)^2+k

at x=0, y= -4, so

-4 = a+k

-20 = 9a + k

k=-2

a=-2

so, y = -2(x-1)^2 - 2

or, y = -2x^2 + 4x - 4

------------------------------

or, if you let y = ax^2 + bx + c,

-20 = 4a - 2b + c

-4 = c

-20 = 16a + 4b + c

a = -2

b = 4

c = -4

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

- algebra -
**Lee**, Monday, October 29, 2012 at 4:41pmThanks for helping I have posted two other questions if you might be able to help

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