Question 139161
the vertex form of a parabolic (quadratic) equation is y-k=a(x-h)^2
__ vertex is (h,k) and a is a measure of the width of the opening of the parabola


using the vertex __ y-11=a(x-4)^2


substituting the y-intercept __ 3-11=a(0-4)^2 __ -8=a(16) __ -1/2=a


y-11=(-1/2)(x-4)^2