CAT 2025 Slot 1 · Quant · Question 13

CAT 2025 Slot 1 previous year question on Coordinate Geometry (Basics), with the answer and a step-by-step solution.

Coordinate Geometry (Basics)Geometry and MensurationMultiple choiceMedium
The \left( x,y \right) coordinates of vertices P, Q and R of a parallelogram PQRS are \left( -3,-2 \right), \left( 1,-5 \right) and \left( 9,1 \right), respectively. If the diagonal SQ intersects the x-axis at \left( a,0 \right), then the value of a is
  1. A
    \frac{13}{4}
  2. B
    \frac{29}{9}
  3. C
    \frac{10}{3}
  4. D
    \frac{27}{7}
Pick an option, then check.
Answer & solution

Answer: Option B

In a parallelogram the diagonals bisect each other, so PR and QS share a midpoint.

Midpoint of PR =\left( \frac{-3+9}{2},\frac{-2+1}{2}\right)=\left( 3,-\frac{1}{2}\right)=A (Let).

The line through Q\left( 1,-5 \right) and A\left( 3,-\frac{1}{2}\right)has slope \frac{-\frac{1}{2}-\left( -5 \right)}{3-1}=\frac{9}{4}, so y+5=\frac{9}{4}\left( x-1 \right).

Setting y=0 because it passes through x axis:

5=\frac{9}{4}\left( x-1 \right),

so x-1=\frac{20}{9} and a=\frac{29}{9}.

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