Solve 3|x + 5| − 3 = 9
Absolute value equation, worked out line by line the way a teacher would write it.
Answer
| Solutions | x = −9, x = −1 |
Step-by-step solution
8 steps-
1 Given3 \left|{x + 5}\right| - 3 = 9
Solve for x.
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2 Isolate the absolute value\left|{x + 5}\right| = 4
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3 Split into two cases: the expression inside the bars is either 4 or -4
|u| is the distance of u from 0. A distance of 4 can be on either side of 0, so the inside is 4 or the opposite of 4, and each case is solved as its own equation.
x + 5 = 4\quad \text{or} \quad x + 5 = -4 -
4 Case 1x + 5 = 4
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5 Subtract 5 from both sides
An equation stays true as long as you do the same thing to both sides, like adding the same weight to both pans of a balance. Adding or subtracting the same amount on both sides moves a term to the other side, where it appears with the opposite sign.
x = -1Move the constant terms to the right.
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6 Case 2x + 5 = -4
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7 Subtract 5 from both sidesx = -9
Move the constant terms to the right.
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8 Check\begin{aligned}x = -9:\quad 9 = 9\quad\checkmark\\ x = -1:\quad 9 = 9\quad\checkmark\end{aligned}
Substituting each solution back makes both sides equal.
Check by substitution
| x | Left side | Right side | |
|---|---|---|---|
| −9 | 9 | 9 | ✓ |
| −1 | 9 | 9 | ✓ |
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