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MathRevolution
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MathRevolution
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MathRevolution
=>

\((a + b)x + 2a - 3b < 0\)

=> \((a + b)x < 3b - 2a\)

=> \(x < \frac{(3b - 2a) }{ (a + b)}\) under the assumption \(a + b > 0\)

Since its solution set is \(x < -(\frac{1}{3})\), we have \(\frac{(3b - 2a) }{ (a + b)} = -(\frac{1}{3})\) or \((-3)(3b - 2a) = a + b.\) Then we have \(6a – 9b = a + b\) or \(a = 2b.\)

Since \(a = 2b\), the inequality \((a - 3b)x + b - 2a > 0\) is equivalent to \((2b - 3b)x + b – 4b > 0\) or \(-bx – 3b > 0\).

Then we have \(bx < -3b\) or \(x < -3.\)

Therefore, A is the answer.
Answer: A

Why did u assume that a+b > 0 & b >0 ? How did u know ? What if this was not the case ?
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MathRevolution
I have commented on your solutions at various places but never received any revert. Could u respond pls ?
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