Solve the Complex Fraction Equation: -7/((x+4)×3-7) = 2/(5+x)

Complex Fractions with Cross-Multiplication

Solve for X:

7(x+4)×37=25+x \frac{-7}{(x+4)\times3-7}=\frac{2}{5+x}

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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
00:42 Carefully open parentheses properly, multiply by each term
01:08 Collect like terms
01:17 Carefully open parentheses properly, multiply by each term
01:27 Arrange the equation so that X is isolated on one side
01:47 Collect like terms
01:54 Isolate X
02:10 And this is 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:

7(x+4)×37=25+x \frac{-7}{(x+4)\times3-7}=\frac{2}{5+x}

2

Step-by-step solution

To solve the given equation, we'll use the approach of cross-multiplication. Let's work through it step by step:

  • Step 1: Simplify the denominators:
    • In (x+4)×37(x+4)\times3-7, first compute the multiplication: (x+4)×3=3x+12(x+4)\times3 = 3x + 12.
    • Subtract 7, obtaining: 3x+127=3x+53x + 12 - 7 = 3x + 5.
  • Step 2: Plug these simplifications back into the equation:
  • 73x+5=25+x\frac{-7}{3x+5} = \frac{2}{5+x}

  • Step 3: Cross-multiply to clear the fractions:
  • 7(5+x)=2(3x+5)-7(5+x) = 2(3x+5)

  • Step 4: Expand both sides:
    • 7×5=35-7 \times 5 = -35 and 7×x=7x-7 \times x = -7x, so the left side is 357x-35 - 7x.
    • For the right side: 2×3x=6x2 \times 3x = 6x and 2×5=102 \times 5 = 10, so it equals 6x+106x + 10.
  • Step 5: Set up the equation from expansions:
  • 357x=6x+10-35 - 7x = 6x + 10

  • Step 6: Solve for x x :
    • Add 7x 7x to both sides to collect x x terms on one side:
    • 35=6x+10+7x-35 = 6x + 10 + 7x

    • This simplifies to: 35=13x+10-35 = 13x + 10.
    • Subtract 10 from both sides:
    • 3510=13x-35 - 10 = 13x

      45=13x-45 = 13x

    • Divide both sides by 13 to solve for x x :
    • x=4513x = \frac{-45}{13}

    • Convert 4513-\frac{45}{13} to a decimal: 3.46-3.46 (rounded to two decimal places).
  • Step 7: Verify:
    • Verify 5+x0 5 + x \neq 0 and 3x+50 3x + 5 \neq 0 based on our found value, ensuring no division by zero. Both conditions are true.

Therefore, the solution to the problem is x=3.46 x = -3.46 .

3

Final Answer

3.46 -3.46

Key Points to Remember

Essential concepts to master this topic
  • Cross-multiplication: When ab=cd \frac{a}{b} = \frac{c}{d} , then ad=bc a \cdot d = b \cdot c
  • Simplify denominators first: (x+4)×37=3x+127=3x+5 (x+4)\times 3-7 = 3x+12-7 = 3x+5
  • Check division by zero: Ensure x53 x \neq -\frac{5}{3} and x5 x \neq -5

Common Mistakes

Avoid these frequent errors
  • Forgetting to simplify complex denominators first
    Don't jump straight to cross-multiplying with (x+4)×37 (x+4)\times 3-7 unsimplified = confusing algebra! This creates messy expressions and calculation errors. Always simplify denominators to 3x+5 3x+5 before cross-multiplying.

Practice Quiz

Test your knowledge with interactive questions

Solve for \( b \):

\( 8-b=6 \)

FAQ

Everything you need to know about this question

Why do I need to simplify the denominator first?

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Simplifying (x+4)×37 (x+4)\times 3-7 to 3x+5 3x+5 makes cross-multiplication much cleaner! Working with the complex form leads to messy algebra and more chances for errors.

What exactly is cross-multiplication?

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Cross-multiplication means if AB=CD \frac{A}{B} = \frac{C}{D} , then A×D=B×C A \times D = B \times C . So 73x+5=25+x \frac{-7}{3x+5} = \frac{2}{5+x} becomes 7(5+x)=2(3x+5) -7(5+x) = 2(3x+5) .

How do I know if my decimal answer is accurate enough?

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For this problem, x=4513=3.46... x = -\frac{45}{13} = -3.46... The question asks for -3.46 (two decimal places). Always check what precision the problem requires!

What if I get division by zero in my answer?

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Before solving, check that your solution won't make any denominator zero. Here, x=3.46 x = -3.46 doesn't equal 5 -5 or 53 -\frac{5}{3} , so we're safe!

Can I solve this without cross-multiplication?

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Yes! You could multiply both sides by (3x+5)(5+x) (3x+5)(5+x) to clear fractions, but cross-multiplication is much faster for equations with two fractions equal to each other.

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