Posted by Lee on Monday, October 29, 2012 at 3:54pm.
you 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
Thanks for helping I have posted two other questions if you might be able to help
Related Questions
math - the points (-9,0) and (19,0) lie on parabola. a.) determine an equation ...
Algebra 2 - I have a question and I can not figure it out. Any answers to the ...
Alg II/Trig - A parabola has a vertex at (0,0); a horizontal axis; and the point...
algebra 2 please check - Write an equation for a parabola with vertex at (-4 , 3...
Math - algebraish - hey how do we convert y=mx+b to standard form? the standard ...
pre cal - find the standard form of the equation of a parabola with the vertex (...
pre cal - What is the center of the conic whose equation is x^2 + 2y^2 - 6x + ...
algebra help please - I notice that other problems are answered in a timely ...
algebra - What is the equation in standard form, of a parabola that models the ...
algebra - What is the equation in standard form of a parabola that models the ...
For Further Reading
