Solve the Rational Equation: 7/(x-5) = 15/(3-x)

Rational Equations with Cross-Multiplication

Solve for X:

7x5=153x \frac{7}{x-5}=\frac{15}{3-x}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:09 First, let's find X.
00:13 Multiply by the common denominator. This helps get rid of fractions.
00:37 Now, simplify everything as much as you can.
00:48 Carefully open the parentheses, and multiply each factor step-by-step.
01:05 Rearrange the equation so one side only has X.
01:24 Next, collect all the like terms together.
01:35 Isolate X by itself on one side of the equation.
01:53 And that's how we find the solution to the problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve for X:

7x5=153x \frac{7}{x-5}=\frac{15}{3-x}

2

Step-by-step solution

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

  • Step 1: Transform the equation to ensure the denominators are handled correctly.
  • Step 2: Apply cross-multiplication to eliminate the fractions.
  • Step 3: Simplify the resulting equation and solve for xx.
  • Step 4: Verify that the solution does not make either denominator zero.

Now, let's work through each step:

Step 1: Recognize that 3x=(x3)3-x = -(x-3), so we can rewrite the equation as:

7x5=15(x3)\frac{7}{x-5}=\frac{15}{-(x-3)}, which simplifies to 7x5=15x3\frac{7}{x-5} = -\frac{15}{x-3}.

Step 2: Apply cross-multiplication:

Multiply both sides to clear the fractions:

7(x3)=15(x5)7 \cdot (x-3) = -15 \cdot (x-5).

Step 3: Distribute and solve for xx:

Expanding both sides, we get: 7x21=15x+757x - 21 = -15x + 75.

Bring all terms involving xx to one side:

7x+15x=75+217x + 15x = 75 + 21.

This simplifies to:

22x=9622x = 96.

Now, solve for xx:

x=9622x = \frac{96}{22}.

Simplify the fraction:

x=4811x = \frac{48}{11}.

Convert to a decimal, if preferred:

x4.36x \approx 4.36.

Step 4: Verify that the solution does not make either denominator zero:

With x=4.36x = 4.36, neither x5x - 5 nor 3x3 - x is zero, so the solution is valid.

Therefore, the solution to the equation is 4.36\boxed{4.36}.

3

Final Answer

4.36 4.36

Key Points to Remember

Essential concepts to master this topic
  • Cross-Multiplication: Multiply diagonally to eliminate fractions completely
  • Technique: For 7x5=153x \frac{7}{x-5} = \frac{15}{3-x} , get 7(3-x) = 15(x-5)
  • Check: Verify denominators aren't zero: x ≠ 5 and x ≠ 3 ✓

Common Mistakes

Avoid these frequent errors
  • Ignoring the sign when rewriting denominators
    Don't treat 3-x the same as x-3 = wrong sign in your equation! Since 3-x = -(x-3), you must include the negative sign. Always rewrite denominators carefully and account for sign changes.

Practice Quiz

Test your knowledge with interactive questions

Solve for X:

\( 6 - x = 10 - 2 \)

FAQ

Everything you need to know about this question

Why do I need to rewrite 3-x as -(x-3)?

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This helps you see the relationship between denominators more clearly! Since 3x=(x3) 3-x = -(x-3) , your equation becomes 7x5=15x3 \frac{7}{x-5} = -\frac{15}{x-3} , making cross-multiplication easier.

What if my answer makes a denominator zero?

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Then it's not a valid solution! Rational equations can't have solutions that make denominators zero because division by zero is undefined. Always check your answer in the original denominators.

Can I just multiply both sides by (x-5)(3-x)?

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Yes! That's another valid method. Multiply every term by (x5)(3x) (x-5)(3-x) to clear both denominators at once. You'll get the same answer as cross-multiplication.

How do I convert 48/11 to a decimal?

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Divide 48 by 11 using long division or a calculator. 4811=4.363636... \frac{48}{11} = 4.363636... which rounds to 4.36 when rounded to two decimal places.

Why is my cross-multiplication giving me a different equation?

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Make sure you're multiplying correctly! For ab=cd \frac{a}{b} = \frac{c}{d} , cross-multiplication gives you a × d = b × c. Double-check which terms you're multiplying together.

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