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Question: Answered & Verified by Expert
If $a, b$ are positive real numbers such that the lines ax $+9 y=5$ and $4 x+b y=3$ are parallel, then the least possible value of $a+b$ is
MathematicsStraight LinesJEE Main
Options:
  • A 13
  • B 12
  • C 8
  • D 6
Solution:
2312 Upvotes Verified Answer
The correct answer is: 12
$\frac{a}{4}=\frac{9}{b} \Rightarrow a b=36$
using $A M \geq G \cdot M$
$\frac{a+b}{2} \geq \sqrt{a b} \Rightarrow a+b \geq 12$

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