Solve the Linear System: 3x - 4y = 10 and 9x - 12y = 15

Linear Systems with Parallel Lines

Choose the correct answer for the following exercise:

{3x4y=109x12y=15 \begin{cases} 3x-4y=10 \\ 9x-12y=15 \end{cases}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve the system of equations
00:04 Multiply by 3 so that we can isolate Y by subtraction
00:16 Now this is the system of equations
00:22 Subtract between the equations
00:34 Collect like terms
00:48 We got an illogical expression, therefore there is no solution
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

Choose the correct answer for the following exercise:

{3x4y=109x12y=15 \begin{cases} 3x-4y=10 \\ 9x-12y=15 \end{cases}

2

Step-by-step solution

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

  • Step 1: Verify if both equations in the system are proportional.
  • Step 2: Determine if they result in a true or false statement when simplified.
  • Step 3: Conclude about the solution set based on the results.

Now, let's work through each step:
Step 1: Start with the system of equations:
{3x4y=109x12y=15\begin{cases} 3x - 4y = 10 \\ 9x - 12y = 15 \end{cases}

Step 2: Check if the second equation is a multiple of the first equation.
Divide each coefficient of the second equation by 3:
- (9x)÷3=3x(9x) \div 3 = 3x
- (12y)÷3=4y(-12y) \div 3 = -4y
- (15)÷3=5(15) \div 3 = 5
Thus, converting: {3x4y=103x4y=5\begin{cases} 3x - 4y = 10 \\ 3x - 4y = 5 \end{cases}

Step 3: We notice that while the left sides of both equations are identical, the right sides differ:
This results in a logical contradiction because 10510 \neq 5.
Thus, these lines are parallel and distinct, indicating that the system has no common points of intersection, hence no solution.

Therefore, the correct conclusion for this system of equations is No solution.

3

Final Answer

No solution

Key Points to Remember

Essential concepts to master this topic
  • Recognition: Check if equations have proportional coefficients but different constants
  • Technique: Divide second equation by 3: 9x12y=15 9x - 12y = 15 becomes 3x4y=5 3x - 4y = 5
  • Check: Compare simplified equations: 3x4y=10 3x - 4y = 10 vs 3x4y=5 3x - 4y = 5 , since 105 10 \neq 5

Common Mistakes

Avoid these frequent errors
  • Assuming proportional coefficients mean infinite solutions
    Don't assume that when left sides are identical, the system has infinite solutions = wrong conclusion! You must check if the right sides are also equal. Always compare both sides after simplification to determine if lines are identical or parallel.

Practice Quiz

Test your knowledge with interactive questions

Solve the following equations:

\( \begin{cases} 2x+y=9 \\ x=5 \end{cases} \)

FAQ

Everything you need to know about this question

How do I know when a system has no solution?

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A system has no solution when the equations represent parallel lines. This happens when the left sides are identical but the right sides are different, like 3x4y=10 3x - 4y = 10 and 3x4y=5 3x - 4y = 5 .

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

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No solution: Parallel lines that never meet (same slope, different y-intercepts)
Infinite solutions: Same line written two ways (identical equations after simplification)

Why can't I just solve this system normally?

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You could try, but you'd quickly see the contradiction! When you eliminate variables, you'd get 10=5 10 = 5 , which is impossible. Recognizing the pattern saves time.

How do I check if coefficients are proportional?

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Divide all terms in one equation by the same number to see if you get the other equation's left side. Here: 9x12y=15 9x - 12y = 15 ÷ 3 gives 3x4y=5 3x - 4y = 5

What does this look like on a graph?

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These equations represent two parallel lines that never intersect. They have the same slope but different y-intercepts, so there's no point that satisfies both equations simultaneously.

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