Question

Which of these equations has a vertex that is the maximum point of parabola? More than one can be chosen. y=-4x^2+ 8x - 19, y=-x^2- 7x + 1, y=8x^2-6x +128, y=3x^2 + 9x - 4

Answer 1

if the coefficient of x^2 < 0, then we're talking maximum

Answer 2

A parabola has a maximum (i.e. concave down, or opens downwards) when the leading coefficient a is negative in the equation
y=ax^2+bx+c
Among the choices, there are two such parabolas.

Answer 3

I think the answers are y+8x^2-6x+128 and y+3x^2 +9x -4. Is this correct?

Answer 4

Negative you want negative x^2

Answer 5

So there is a bit of misunderstanding here that we should clear up

Answer 6

Oh! Ok so it would be the first 2 answers then?

Answer 7

yes
and what you did in your answer above is move other terms to the same side as y and you don't want to go there

Answer 8

I misread x^2 < 0 as x^2 > 0. Thank you so much (:

Answer 9

yw

Answer 10

Check the sign only when you transform the equation to the following form:
y=ax^2+bx+c
then if a is negative, there is a maximum.