Find the set of solutions for x in the inequality x+2x+1>2x+93x+4 when x=−2,x=29.
A number or a short expression. Spacing and $ signs are ignored.
Solution
There are 3 possible cases of x: 1) −29<x, 2) 29≤x≤−2, 3) −2<x. For the cases (1) and (3), x+2 and 2x+9 are both positive or negative, so the following operation can be carried out without changing the inequality sign: x+2x+1⇒2x2+11x+9⇒0>2x+93x+4>3x2+10x+8>x2−x−1 The inequality holds for all 21−5<x<21+5. The initial conditions were −29<x or −2<x. The intersection of these three conditions occurs when 21−5<x<21+5. Case (2) is 29≤x≤−2. For all x satisfying these conditions, x+2<0 and 2x+9>0. Then the following operations will change the direction of the inequality: x+2x+1⇒2x2+11x+9⇒0>2x+93x+4<3x2+10x+8<x2−x−1 The inequality holds for all x<21−5 and 21+5<x. The initial condition was 2−9≤x≤−2. Hence the intersection of these conditions yields all x such that 2−9≤x≤−2. Then all possible cases of x are 2−9≤x≤−2∪21−5<x<21+5.
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