Solve the System of Equations with Fractions: Find the Values of X and Y

Systems of Equations with Variable Substitution

3x+3y=2 \frac{3}{x}+\frac{3}{y}=2

9x4y=7 \frac{9}{x}-\frac{4}{y}=-7

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:04 Let's multiply one of the equations by 3, so we can subtract between them
00:16 Now let's subtract between the equations
00:22 Let's reduce what we can
00:31 Let's collect like terms
00:43 Let's isolate Y
00:54 This is the value of Y
01:00 Now let's substitute Y to find the value of X
01:13 Let's isolate X
01:32 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

3x+3y=2 \frac{3}{x}+\frac{3}{y}=2

9x4y=7 \frac{9}{x}-\frac{4}{y}=-7

2

Step-by-step solution

To solve this system of linear equations, follow these steps:

  • Step 1: Examine and rearrange the first equation 3x+3y=2 \frac{3}{x} + \frac{3}{y} = 2 .
  • Step 2: Express one variable in terms of the other. We can isolate 3x\frac{3}{x} to get 3x=23y\frac{3}{x} = 2 - \frac{3}{y}.
  • Step 3: Substitute 3x=23y\frac{3}{x} = 2 - \frac{3}{y} into the second equation 9x4y=7\frac{9}{x} - \frac{4}{y} = -7.
  • Step 4: Replace 9x\frac{9}{x} with 3(23y)3\left(2 - \frac{3}{y}\right) leading to 3(23y)4y=73\left(2 - \frac{3}{y}\right) - \frac{4}{y} = -7.
  • Step 5: Simplify the equation: Distribute 33 into 23y2 - \frac{3}{y} to obtain (69y)4y=7(6 - \frac{9}{y}) - \frac{4}{y} = -7.
  • Step 6: Combine the terms to get 613y=76 - \frac{13}{y} = -7.
  • Step 7: Isolate 13y\frac{13}{y}: 13y=13\frac{13}{y} = 13.
  • Step 8: Solve for yy: Multiply both sides by yy, leading to 13=13y13 = 13y, hence y=1y = 1.
  • Step 9: Substitute y=1y = 1 back into 3x=23y\frac{3}{x} = 2 - \frac{3}{y}, resulting in 3x=23\frac{3}{x} = 2 - 3, or 3x=1\frac{3}{x} = -1.
  • Step 10: Solve for xx: Multiply both sides by xx, leading to 3=x3 = -x, thus x=3x = -3.

Therefore, the solution to the system of equations is x=3\boldsymbol{x = -3} and y=1\boldsymbol{y = 1}.

The correct choice among the given answer choices is the third option: x=3,y=1\boldsymbol{x = -3, y = 1}.

3

Final Answer

x=3,y=1 x=-3,y=1

Key Points to Remember

Essential concepts to master this topic
  • Substitution Rule: Express one variable in terms of the other first
  • Technique: Replace 9x \frac{9}{x} with 33x 3 \cdot \frac{3}{x} for easier substitution
  • Check: Verify 33+31=1+3=2 \frac{3}{-3} + \frac{3}{1} = -1 + 3 = 2

Common Mistakes

Avoid these frequent errors
  • Forgetting to multiply coefficients when substituting
    Don't substitute 3x=23y \frac{3}{x} = 2 - \frac{3}{y} directly into 9x \frac{9}{x} = wrong equation! This ignores that 9x=33x \frac{9}{x} = 3 \cdot \frac{3}{x} . Always multiply the entire substituted expression by the correct coefficient.

Practice Quiz

Test your knowledge with interactive questions

\( \begin{cases} x+y=8 \\ x-y=6 \end{cases} \)

FAQ

Everything you need to know about this question

Why do we use substitution instead of elimination for this system?

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With fractional coefficients like 3x \frac{3}{x} and 3y \frac{3}{y} , substitution is often cleaner than elimination. Notice how 9x=33x \frac{9}{x} = 3 \cdot \frac{3}{x} makes substitution natural!

How do I handle the relationship between 3x \frac{3}{x} and 9x \frac{9}{x} ?

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Recognize that 9x=33x \frac{9}{x} = 3 \cdot \frac{3}{x} ! This connection is key for substitution. Whatever expression equals 3x \frac{3}{x} , multiply it by 3 to get 9x \frac{9}{x} .

What if I get negative values for x and y?

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Negative solutions are perfectly valid! Many systems have negative answers. Just be extra careful with signs during substitution and always verify your solution.

Can I solve this by making u = 1/x and v = 1/y substitutions?

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Yes! This transforms the system into linear equations in u and v: 3u+3v=2 3u + 3v = 2 and 9u4v=7 9u - 4v = -7 . Then convert back to find x and y.

How do I check my answer when fractions are involved?

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Substitute your values into both original equations. For x=3,y=1 x = -3, y = 1 : First equation gives 33+31=1+3=2 \frac{3}{-3} + \frac{3}{1} = -1 + 3 = 2

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