★ f(x) = (2x - 1)(2 - x)
BXD:
x | -∞ 1/2 2 +∞
2x -1 | - 0 + 0 +
2 - x | + | + 0 -
f(x) | - 0 + 0 -
KL:
f(x) > 0 ; mọi x € (1/2:2)
f(x) < 0 ; mọi x € (-∞;1/2) U (2;+∞)
f(x) = 0 ; khi x = 1/2 ; x = 2
★ f(x) = (2x - 1)(x + 3)
BXD:
x | -∞ -3 1/2 +∞
2x - 1| - | - 0 +
x + 3 | - 0 + | +
f(x) | + 0 - 0 +
KL:
f(x) > 0 ; mọi x € (-∞;-3) U (1/2;+∞)
f(x) < 0 ; mọi x € (-3:1/2)
f(x) = 0 ; khi x = -3 ; x = 1/2
