Solve for X in the Equation x/(3+2x) = 1/5: Rational Expression Problem

Rational Equations with Cross-Multiplication Method

Solve for X:

x3+2x=15 \frac{x}{3+2x}=\frac{1}{5}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:04 Multiply by denominators to eliminate fractions
00:26 Simplify as much as possible
00:40 Arrange the equation so that X is isolated on one side
00:58 Isolate X
01:07 Simplify as much as possible
01:12 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve for X:

x3+2x=15 \frac{x}{3+2x}=\frac{1}{5}

2

Step-by-step solution

To solve the equation x3+2x=15\frac{x}{3+2x} = \frac{1}{5}, we will perform the following steps:

  • Step 1: Cross-multiply to eliminate the fractions.
  • Step 2: Simplify the resulting equation and solve for xx.

Now, let's work through these steps:

Step 1: Cross-multiply the equation x3+2x=15\frac{x}{3+2x} = \frac{1}{5} to obtain:

5x=1(3+2x)5x = 1(3 + 2x)

Step 2: Distribute the 1 on the right-hand side:

5x=3+2x5x = 3 + 2x

Subtract 2x2x from both sides to begin isolating xx:

5x2x=35x - 2x = 3

3x=33x = 3

Divide both sides by 3 to solve for xx:

x=33x = \frac{3}{3}

x=1x = 1

Therefore, the solution to the problem is 1\boxed{1}.

The correct answer, matching the given choices, is therefore choice 22.

3

Final Answer

1 1

Key Points to Remember

Essential concepts to master this topic
  • Cross-Multiplication Rule: When ab=cd \frac{a}{b} = \frac{c}{d} , then ad=bc ad = bc
  • Distribution Technique: From 5x=1(3+2x) 5x = 1(3 + 2x) distribute to get 5x=3+2x 5x = 3 + 2x
  • Verification Check: Substitute x=1 x = 1 back: 13+2(1)=15 \frac{1}{3+2(1)} = \frac{1}{5}

Common Mistakes

Avoid these frequent errors
  • Incorrectly cross-multiplying complex expressions
    Don't cross-multiply x3+2x=15 \frac{x}{3+2x} = \frac{1}{5} as x5=13+2x x \cdot 5 = 1 \cdot 3+2x = missing parentheses around the denominator! This gives 5x=3+2x 5x = 3+2x instead of 5x=1(3+2x) 5x = 1(3+2x) . Always treat the entire denominator as one unit when cross-multiplying.

Practice Quiz

Test your knowledge with interactive questions

Solve for X:

\( x - 3 + 5 = 8 - 2 \)

FAQ

Everything you need to know about this question

What exactly is cross-multiplication?

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Cross-multiplication is a shortcut for solving equations with one fraction on each side. When you have ab=cd \frac{a}{b} = \frac{c}{d} , you multiply diagonally: a times d equals b times c.

Why do I need to check my answer?

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Rational equations can sometimes produce extraneous solutions that make denominators zero. Always substitute back to ensure your answer doesn't create division by zero!

What if the denominator contains my variable?

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That's exactly what makes this a rational equation! Just remember to keep the entire denominator together when cross-multiplying, like treating (3+2x) (3+2x) as one unit.

Can I solve this without cross-multiplying?

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Yes! You could multiply both sides by 5(3+2x) 5(3+2x) to clear fractions. But cross-multiplication is usually faster and cleaner when you have this fraction-equals-fraction setup.

How do I know when to use parentheses?

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  • Always put parentheses around multi-term denominators
  • In our problem: 5x=1(3+2x) 5x = 1(3+2x) not 5x=13+2x 5x = 1 \cdot 3 + 2x
  • This ensures you distribute correctly!

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