# parabola HW help plz

• Apr 6th 2008, 01:27 PM
gumi
parabola HW help plz
A, write an equation whose graph is a parabola whose vertex is (3/4,-3)

B, write an equation whose graph is a parabola that opens downward and has an axis of symmetry x=-4

C, Write an equation whose graph is a parabola opens upward and has a y-intercept of -1/2

D, Write an equation whose graph is a parabola whose vertex is (-3,4) with a y intercept of 1
• Apr 6th 2008, 01:37 PM
Mathstud28
OK here is what you do
A. the equation for a parabola with vertex $(h,k)$...is $y=a(x-h)^2+k$...so for $\frac{3}{4},-3)$...is $y=\bigg(x-\frac{3}{4}\bigg)^2-3$

B.the equation for a line facing down with its axis of symmetry at 4 is $y=-a(x+4)^2+k$

C.one of the possibilities $y=x^2-\frac{1}{2}$

D.to do this you need to set up your equation [tex]y=a(x+3)^2+4...I know...now all you have to do is say is put in your values $1=a(0+3)^2+4$ and solve for a...so you get $a=\frac{-1}{3}$...so your equation is $y=\frac{-(x+3)^2}{3}+4$