SOLUTION: What values of x satisfy |x - 4| + 2(x + 3) <= 11 + 5|x + 7| + 3x + 8. Express your answer in interval notation.

Algebra ->  Absolute-value -> SOLUTION: What values of x satisfy |x - 4| + 2(x + 3) <= 11 + 5|x + 7| + 3x + 8. Express your answer in interval notation.      Log On


   



Question 1209364: What values of x satisfy |x - 4| + 2(x + 3) <= 11 + 5|x + 7| + 3x + 8.
Express your answer in interval notation.

Answer by greenestamps(13214) About Me  (Show Source):
You can put this solution on YOUR website!


abs%28x-4%29%2B2%28x%2B3%29%3C=11%2B5abs%28x%2B7%29%2B3x%2B8

Simplify the inequality....

abs%28x-4%29%2B2x%2B6%3C=5abs%28x%2B7%29%2B3x%2B19
abs%28x-4%29-5abs%28x%2B7%29%3C=x%2B13

The behavior of the function changes when the arguments of the absolute value expressions are equal to 0 -- at x=4 and x=-7. That divides the number line into three intervals: (-infinity,-7], [-7,4], and [4,infinity)

Find the value on each interval that satisfy the inequality.

(1) (-infinity,-7]

On this interval, abs%28x-4%29=-x%2B4 and abs%28x%2B7%29=-x-7

%28-x%2B4%29-5%28-x-7%29%3C=x%2B13
-x%2B4%2B5x%2B35%3C=x%2B13
4x%2B39%3C=x%2B13
3x%3C=-26
x%3C=-26%2F3

Of the values of x on the given interval (-infinity,-7], the ones that satisfy the inequality are those less than or equal to -26/3.

First part of solution set: (-infinity,-26/3]

(2) [-7,4]

On this interval, abs%28x-4%29=-x%2B4 and abs%28x%2B7%29=x%2B7

%28-x%2B4%29-5%28x%2B7%29%3C=x%2B13
-x%2B4-5x-35%3C=x%2B13
-6x-31%3C=x%2B13
7x%3E=-44
x%3E=-44%2F7

Of the value of x on the given interval [-7,4], the ones that satisfy the inequality are those greater than or equal to -44/7.

Second part of solution set: [-44/7,4]

(3) [4,infinity)

On this interval, abs%28x-4%29=x-4 and abs%28x%2B7%29=x%2B7

%28x-4%29-5%28x%2B7%29%3C=x%2B13
x-4-5x-35%3C=x%2B13
-4x-39%3C=x%2B13
5x%3E=-52
x%3E=-52%2F5

All of the values of x on the given interval [4,infinity) are greater than or equal to -52/5.

Third part of solution set: [4,infinity)

ANSWER: the complete solution set is (-infinity,-26/3] U [-44/7,infinity)

The simplified form of the inequality I used is abs%28x-4%29-5abs%28x%2B7%29%3C=x%2B13, which is equivalent to abs%28x-4%29-5abs%28x%2B7%29-%28x%2B13%29%3C=0.

Here is a graph of that function showing the value is less than or equal to 0 on (-infinity,-26/3] U [-44/7,infinity).

graph%28400%2C400%2C-10%2C10%2C-10%2C10%2Cabs%28x-4%29-5abs%28x%2B7%29-%28x%2B13%29%29