- #1
mathdad
- 1,283
- 1
Solve the inequality.
2x^2 + 7x + 5 > 0
Factor LHS.
2x^2 + 2x + 5x + 5 > 0
2x(x + 1) + 5(x + 1) > 0
(2x + 5)(x + 1) > 0
2x + 5 = 0
2x = -5
x = -5/2
x + 1 = 0
x = -1
Plot x = -5/2 and x = -1 on a number line.
<--------(-5/2)----------(-1)----------->
Pick a number from each interval.
Let x = -4 for (-infinity, -5/2).
Let x = -1/2 for (-5/2, -1).
Let x = 0 for (-1, infinity).
Do I avaluate the chosen numbers per interval in the original question or the factored form?
2x^2 + 7x + 5 > 0
Factor LHS.
2x^2 + 2x + 5x + 5 > 0
2x(x + 1) + 5(x + 1) > 0
(2x + 5)(x + 1) > 0
2x + 5 = 0
2x = -5
x = -5/2
x + 1 = 0
x = -1
Plot x = -5/2 and x = -1 on a number line.
<--------(-5/2)----------(-1)----------->
Pick a number from each interval.
Let x = -4 for (-infinity, -5/2).
Let x = -1/2 for (-5/2, -1).
Let x = 0 for (-1, infinity).
Do I avaluate the chosen numbers per interval in the original question or the factored form?