Solving Absolute Value Equations: Finding x in |x+3|=|2x+6|

Absolute Value Equations with Equal Expressions

∣x+3∣=∣2x+6∣ |x+3|=|2x+6|

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1

Understand the problem

∣x+3∣=∣2x+6∣ |x+3|=|2x+6|

2

Step-by-step solution

To solve the equation ∣x+3∣=∣2x+6∣ |x+3| = |2x+6| , we need to consider the properties of absolute values and analyze the cases for different ranges of x x .

The equation ∣x+3∣=∣2x+6∣ |x+3| = |2x+6| implies two possibilities based on absolute value properties:

  • x+3=2x+6 x+3 = 2x+6
  • x+3=−(2x+6) x+3 = -(2x+6)

Let's solve each case:

Case 1: x+3=2x+6 x+3 = 2x+6

Simplify the equation:
x+3=2x+6 x + 3 = 2x + 6
Move x x to the other side:
3=x+6 3 = x + 6
Subtract 6 from both sides:
x=−3 x = -3

Case 2: x+3=−(2x+6) x+3 = -(2x+6)

Simplify the equation:
x+3=−2x−6 x+3 = -2x-6
Add 2x 2x to both sides:
3x+3=−6 3x + 3 = -6
Subtract 3 from both sides:
3x=−9 3x = -9
Divide both sides by 3:
x=−3 x = -3

In both cases, we find that x=−3 x = -3 . However, we need to verify if x=−3 x = -3 satisfies the original equation:

Substitute x=−3 x = -3 into the original equation:
∣x+3∣=∣2x+6∣ |x+3| = |2x+6|
∣−3+3∣=∣2(−3)+6∣ |-3+3| = |2(-3)+6|
∣0∣=∣−6+6∣ |0| = |-6+6|
0=0 0 = 0

Therefore, x=−3 x = -3 satisfies the equation. The solution to the problem is x=−3 x = -3 .

In conclusion, the correct answer is x=−3 x = -3 .

3

Final Answer

x=−3 x=-3

Key Points to Remember

Essential concepts to master this topic
  • Property: |A| = |B| means A = B or A = -B
  • Technique: Solve x+3 = 2x+6 and x+3 = -(2x+6) separately
  • Check: Substitute x = -3: |-3+3| = |2(-3)+6| → 0 = 0 ✓

Common Mistakes

Avoid these frequent errors
  • Only solving one case instead of both
    Don't just solve x+3 = 2x+6 and ignore the negative case = missing solutions! Absolute value equations can have multiple solutions or the same solution from both cases. Always solve both A = B and A = -B cases completely.

Practice Quiz

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\( \left|x\right|=3 \)

FAQ

Everything you need to know about this question

Why do I need to solve two separate equations?

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Because absolute value represents distance, which is always positive! When |A| = |B|, either both expressions are equal or they're opposites of each other.

What if both cases give me the same answer?

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That's completely normal! Sometimes both cases lead to the same solution, like in this problem where both give x=−3 x = -3 . You still need to check both cases to be thorough.

How do I know which case to use first?

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It doesn't matter which order you solve them! Start with whichever case looks easier to you. Just make sure you solve both cases completely.

Do I always get exactly one solution?

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Not always! Absolute value equations can have no solution, one solution (like this problem), or two different solutions. Always solve both cases to find out.

What does it mean when I get 0 = 0?

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When you substitute your answer and get 0=0 0 = 0 , that's perfect verification! It means your solution is absolutely correct.

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