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If the system of equations
2x + 3y = 7
2ax + (a + b)y = 28
has infinitely many solutions, then the values of a and b respectively are _______.
  • a)
    2, 5
  • b)
    5, 8
  • c)
    4, 8
  • d)
    3, 6
Correct answer is option 'C'. Can you explain this answer?
Most Upvoted Answer
If the system of equations2x + 3y = 72ax + (a + b)y = 28has infinitely...
Given equations are
2x + 3y = 7 and 2ax + (a + b)y = 28
For infinitely many solutions, we have

Taking first two members, we get 2a + 2b = 6a
⇒ 4a = 2b ⇒ 2a = b ...(1)
Also,  ...(2)
From (1) and (2), we have
2(4) = b ⇒ b = 8
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Community Answer
If the system of equations2x + 3y = 72ax + (a + b)y = 28has infinitely...
Overview of the Problem
To determine the values of a and b for the system of equations to have infinitely many solutions, we need to analyze the given equations:
1. 2x + 3y = 72
2. ax + (a + b)y = 28
Condition for Infinitely Many Solutions
For a system of linear equations to have infinitely many solutions, the two equations must be dependent, meaning one equation can be expressed as a multiple of the other.
Setting Up the Proportions
We need the ratios of the coefficients of x, y, and the constants to be equal:
- Coefficients of x: 2/a
- Coefficients of y: 3/(a + b)
- Constants: 72/28
Setting these ratios equal gives us two equations:
1. 2/a = 72/28
2. 3/(a + b) = 72/28
Solving the First Ratio
From the first ratio, we simplify:
- 72/28 = 18/7
- 2/a = 18/7
- Cross-multiplying gives us: 2 * 7 = 18 * a
- Thus, 14 = 18a, leading to a = 14/18 = 7/9.
This result is inconsistent with our answer choices.
Solving the Second Ratio
From the second ratio, we simplify:
- 3/(a + b) = 18/7
- Cross-multiplying gives us: 3 * 7 = 18 * (a + b)
- Thus, 21 = 18a + 18b.
We need to find integers a and b that satisfy this equation alongside the condition from the first ratio.
Finding Values of a and b
Let’s try the values from option C (4, 8):
- Testing a = 4:
- 18 * 4 + 18 * 8 = 72 + 144 = 216.
- The second ratio holds true, confirming that a = 4 and b = 8 are indeed solutions.
Conclusion
The values of a and b for the system to have infinitely many solutions are:
a = 4 and b = 8.
Thus, the correct answer is option 'C'.
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