Solve the Rational Equation: 5/(8-x) = 3/(2x)

Cross-multiplication with Rational Equations

Solve for X:

58x=32x \frac{5}{8-x}=\frac{3}{2x}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 We want to isolate the unknown X
00:07 Multiply by both denominators to eliminate fractions
00:17 Properly open parentheses, multiply by each factor
00:24 Arrange the equation so that one side has only the unknown X
00:37 Isolate the unknown X
00:42 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:

58x=32x \frac{5}{8-x}=\frac{3}{2x}

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify that the given equation is 58x=32x\frac{5}{8-x} = \frac{3}{2x}.
  • Step 2: Cross-multiply to eliminate the fractions.
  • Step 3: Solve the resulting linear equation.
  • Step 4: Check for any restrictions on xx.

Now, let's work through each step:

Step 1: We have the equation:

58x=32x\frac{5}{8-x} = \frac{3}{2x}

Step 2: Cross-multiply to get:

52x=3(8x)5 \cdot 2x = 3 \cdot (8-x)

This simplifies to:

10x=243x10x = 24 - 3x

Step 3: Solve for xx by isolating it on one side of the equation. Add 3x3x to both sides:

10x+3x=2410x + 3x = 24

This simplifies to:

13x=2413x = 24

Now, divide both sides by 13:

x=2413x = \frac{24}{13}

Step 4: Verify that this value does not make any of the original denominators zero. For x=2413x = \frac{24}{13}, the terms 8x8-x and 2x2x are well-defined, and neither is zero:

82413=80132413=561308 - \frac{24}{13} = \frac{80}{13} - \frac{24}{13} = \frac{56}{13} \neq 0

2×2413=481302 \times \frac{24}{13} = \frac{48}{13} \neq 0

No issues arise from substituting back, so our solution is valid.

Therefore, the solution to the problem is x=2413 x = \frac{24}{13} , which corresponds to choice 3.

3

Final Answer

2413 \frac{24}{13}

Key Points to Remember

Essential concepts to master this topic
  • Cross-multiply Rule: When one fraction equals another, cross products are equal
  • Technique: 58x=32x \frac{5}{8-x} = \frac{3}{2x} becomes 5(2x)=3(8x) 5(2x) = 3(8-x)
  • Check Domain: Verify denominators aren't zero: x0 x \neq 0 and x8 x \neq 8

Common Mistakes

Avoid these frequent errors
  • Forgetting to check domain restrictions
    Don't just solve algebraically and stop = invalid solutions that make denominators zero! This creates undefined expressions in the original equation. Always check that your answer doesn't make any denominator equal to zero.

Practice Quiz

Test your knowledge with interactive questions

\( \frac{-y}{5}=-25 \)

FAQ

Everything you need to know about this question

What exactly does cross-multiplication mean?

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Cross-multiplication means multiplying the numerator of each fraction by the denominator of the other. So 58x=32x \frac{5}{8-x} = \frac{3}{2x} becomes 52x=3(8x) 5 \cdot 2x = 3 \cdot (8-x) .

Why do I need to check if denominators equal zero?

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Division by zero is undefined in mathematics! If your solution makes any denominator zero, it's not actually a valid solution to the original equation. Always verify before finalizing your answer.

What if I get a negative answer?

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Negative solutions are perfectly valid for rational equations! Just make sure to substitute back carefully and check that all denominators remain non-zero.

Can I solve this by finding a common denominator instead?

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Yes, but cross-multiplication is usually faster when you have one fraction equal to another fraction. Common denominators work better when you have multiple fractions being added or subtracted.

How do I verify my answer is correct?

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  • Substitute x=2413 x = \frac{24}{13} into both sides
  • Calculate: 582413=58013=6580 \frac{5}{8-\frac{24}{13}} = \frac{5}{\frac{80}{13}} = \frac{65}{80}
  • And: 322413=34813=3948 \frac{3}{2 \cdot \frac{24}{13}} = \frac{3}{\frac{48}{13}} = \frac{39}{48}
  • Both simplify to the same decimal value!

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