SOLUTION: |x+2|<2x+7

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Question 1049247: |x+2|<2x+7
Found 3 solutions by Alan3354, stanbon, ikleyn:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
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Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
|x+2|<2x+7
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-(2x+7) < x+2 < 2x+7
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-2x-7 < x+2 < 2x+7
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-3x-9 < 0 < x+5
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-3x-9 < 0 and x+5 > 0
3x+9 > 0 and x > -5
3x > -9 and x > -5
x > -3 and x > -5
Ans: x > -3
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Cheers,
Stan H.
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Answer by ikleyn(52858) About Me  (Show Source):
You can put this solution on YOUR website!
.
|x+2|<2x+7.
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|x+2|<2x+7.           (1)

1.  If x+2 >= 0, then  |x+2| = x+2.

    Hence, in the domain x >= -2 the inequality (1) takes the form

    x + 2 < 2x + 7,   or  2-7 < x,  which is  x > -5.

    In other words, in the domain x >= -2 the solution set is x > -5.
    Thus for the domain x > -2 the solution set is the intersection [-2,infinity)  and  (-5,infinity), i.e.  [-2,infinity).


2.  If x+2 < 0, then  |x+2| = -(x+2).

    Hence, in the domain x < -2 the inequality (1) takes the form

    -(x + 2) < 2x + 7,   or  -x - 2 < 2x +7,  or  -2-7 < 3x,  or  -9 < 3x, which is  x > -3.

    In other words, in the domain x < -2 the solution set is x > -3.
    Thus for the domain x < -2 the solution set is the intersection (-infinity,-2)  and  (-3,infinity), i.e.  (-3,-2).


3.  Finally, combining these two cases, we obtain the solution set as  (-3,-2) U [-2,infinity,  i.e.  (-3,infinity).

Answer. The solution set to inequality (1) is (-3,infinity).



Plots y = |x+2| and y = 2x+7