Solve the Linear Equation: 3x - y = -5 and 9x - 3y = -15 for Consistency

Systems of Linear Equations with Dependent Lines

3xy=5 3x-y=-5

9x3y=15 9x-3y=-15

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 Let's multiply one of the equations by 3, so we can subtract between them
00:18 Now let's subtract between the equations
00:31 Let's group like terms
00:48 There are infinite solutions
00:56 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

3xy=5 3x-y=-5

9x3y=15 9x-3y=-15

2

Step-by-step solution

To solve this system of equations, we need to determine the relationship between the two equations. The given equations are:

3xy=53x - y = -5

9x3y=159x - 3y = -15

Let's examine the second equation:

Notice that if we multiply the first equation by 3, we obtain:

3(3xy)=3(5)3(3x - y) = 3(-5)

which simplifies to:

9x3y=159x - 3y = -15

This is exactly the same as the second given equation. Thus, the second equation is a multiple of the first equation, indicating that they represent the same line in the coordinate plane.

When two equations represent the same line, any point on this line will satisfy both equations. Therefore, there are infinitely many solutions to this system. That is, there are infinitely many points (x,y)(x, y) that can satisfy both equations.

Therefore, the solution to the problem is Infinite solutions.

3

Final Answer

Infinite solutions

Key Points to Remember

Essential concepts to master this topic
  • Dependent System: When one equation is a multiple of another
  • Detection Method: Multiply first equation by 3: 3(3xy)=9x3y 3(3x - y) = 9x - 3y
  • Verification: Check if coefficients and constants scale proportionally: 3:1 = 9:3 ✓

Common Mistakes

Avoid these frequent errors
  • Attempting to solve dependent equations as if they're independent
    Don't use elimination or substitution when equations are multiples = wasted time and confusion! This misses that they represent the same line. Always check if one equation is a multiple of another first.

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

How can I tell if a system has infinite solutions?

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Look for dependent equations - when one equation is a multiple of another. If multiplying equation 1 by some number gives you equation 2 exactly, then they're the same line with infinite solutions.

What's the difference between no solution and infinite solutions?

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No solution: parallel lines that never meet. Infinite solutions: the same line written in different forms. Check if the ratios of coefficients match!

Why does multiplying by 3 help me see the relationship?

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Multiplying reveals if equations are equivalent. When 3(3xy=5) 3(3x - y = -5) gives exactly the second equation, they represent identical lines in the coordinate plane.

Can I still find specific x and y values?

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With infinite solutions, you can't find one specific pair. Instead, express y in terms of x: y=3x+5 y = 3x + 5 . Any point on this line works!

What if the equations look completely different?

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Don't be fooled by appearance! Always check proportionality. Equations like 2x+4y=6 2x + 4y = 6 and x+2y=3 x + 2y = 3 are actually the same line.

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