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Question: Answered & Verified by Expert
If the mid point between the points $(a+b, a-b)$ and $(-a, b)$ lies on the line $a x+b y=k$, what is $k$ equal to?
MathematicsStraight LinesNDANDA 2012 (Phase 1)
Options:
  • A $\mathrm{a} / \mathrm{b}$
  • B $\mathrm{a}+\mathrm{b}$
  • C ab
  • D $a-b$
Solution:
1643 Upvotes Verified Answer
The correct answer is: ab
Given points are $(a+b, a-b)$ and $(-a, b)$ Mid point is $\left(\frac{a+b-a}{2}, \frac{a-b+b}{2}\right)=\left(\frac{b}{2}, \frac{a}{2}\right)$
Since, it lies on $a x+b y=k$ $a\left(\frac{b}{2}\right)+b\left(\frac{a}{2}\right)=k \Rightarrow k=a b$

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