The increase and decrease of quadratic function f (x) = AX2 + BX + C (a < 0) in the interval [- B2A, + ∞) is judged and proved according to the definition

The increase and decrease of quadratic function f (x) = AX2 + BX + C (a < 0) in the interval [- B2A, + ∞) is judged and proved according to the definition

Let x1, X2 ∈ [{B2A, + ∞) and let f (x1, X2 ∈ [{B2A, + ∞) and (x1 ＜ X2, then f (x1) - f (x1) - f (x2) = a (x12-x22-x22) + B (x1-x) is a decreasing function on [{B2A, + ∞) [{B2A, + ∞) let x1, X2 ∈ [{B2A, + ∞ [{B2A, + ∞) [{[{B2A, + ∞} [{B2A,} [{B2A,} {B2A {B2A, {f (x1) - f (x1) - f (x1) - f (x1) - f (x2) - f (x) \\\\\\\\\\\\\\c (a) 0) is a decreasing function in the interval [− B 2a, + ∞)