quadratic functions?

Question

how to you decide whether it is a maxiumum or a minimum?

Answer 1

y=ax^2+bx+c
When a is negative the parabola opens down so the parabola has a max at the vertex.
When a is positive the parabola opens up so the parabola has a min at the vertex.

Answer 2

For functions y= f(x) with a positive x^2 coefficient, the result of taking dy/dx and setting it equal to zero will yield a minimum.

Answer 3

When the first derivative is zero, it is a point of inflection. If the second derivative is positive, it's a minimum; if negative, it's a maximum; if zero, neither.

KrazyKyngeKorny
(Krazy, not stupid)