Solve for X in the Equation: x + 9 = 15

Q: Why do I subtract 9 from both sides instead of just the left?

An equation is like a balanced scale. Whatever you do to one side, you must do to the other to keep it balanced. If you only subtract from one side, the equation becomes unequal!

Q: What if I added 9 to both sides instead?

That would give you $ x + 18 = 24 $, which makes the problem harder, not easier! Always use the opposite operation to isolate the variable.

Q: What does 'isolate the variable' mean?

It means getting the variable by itself on one side of the equation. So instead of $ x + 9 = 15 $, you want just $ x = 6 $.

Linear Equations with Single Variable Isolation

Solve for X:

$x + 9 = 15$

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Understand the problem

Solve for X:

$x + 9 = 15$

Step-by-step solution

Step-by-step solution:

1. Begin with the equation: $x + 9 = 15$

2. Subtract 9 from both sides: $x + 9 - 9 = 15 - 9$ , which simplifies to $x = 6$

Final Answer

Key Points to Remember

Essential concepts to master this topic

Inverse Operations: Use subtraction to undo addition on both sides
Technique: Subtract 9 from both sides: 15 - 9 = 6
Check: Substitute back into original equation: 6 + 9 = 15 ✓

Common Mistakes

Avoid these frequent errors

Subtracting from only one side of the equation
Don't subtract 9 from just the left side = x = 15! This breaks the balance of the equation and gives the wrong answer. Always perform the same operation on both sides to maintain equality.

Practice Quiz

Test your knowledge with interactive questions

$$ x+7=14 $$

$x=\text{?}$

FAQ

Everything you need to know about this question

Why do I subtract 9 from both sides instead of just the left?

An equation is like a balanced scale. Whatever you do to one side, you must do to the other to keep it balanced. If you only subtract from one side, the equation becomes unequal!

What if I added 9 to both sides instead?

That would give you $x + 18 = 24$ , which makes the problem harder, not easier! Always use the opposite operation to isolate the variable.

How do I know which operation to use?

Look at what's being done to the variable. Since 9 is being added to x, use subtraction to undo it. Addition and subtraction are opposites!

Can I solve this equation differently?

This is the most direct method! You could add negative numbers or use other approaches, but subtracting 9 from both sides is the clearest and most straightforward way.

What does 'isolate the variable' mean?

It means getting the variable by itself on one side of the equation. So instead of $x + 9 = 15$ , you want just $x = 6$ .

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