Given `f(x)=-4x^2+40x-105` :
Write in vertex form `f(x)=a(x-h)^2+k` by completing the square.
(a) The vertex is at `(h,k)` or `(5,-5)`
(b) The domain is all real numbers since this is a polynomial.
(c) The range is `y<=-5` or `(-oo,-5]`
(d) The y-intercept is found by setting x=0; the y-intercept is -105
(e) There are no x-intercepts. The graph is a parabola (it is a quadratic function) opening down (since a=-5) and the vertex is beneath the x-axis, thus there are no x-intercepts.
** If you use the quadratic formula you get the discriminant `b^2-4ac=40^2-4(-4)(-105)=-80` . Since the discriminant is less than 0 there are no real solutions thus no intercepts.