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Straight Lines and Pair of Straight Lines question

2018 · Shift 0 · Q37
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Straight Lines and Pair of Straight Lines question

2018 · Shift 0 · Q37

JEE MainMathematicsStraight Lines and Pair of Straight LinesMCQ+4 / −1
A straight line through a fixed point (2, 3) intersects the coordinate axes at distinct points P and Q. If O is the origin and the rectangle OPRQ is completed, then the locus of R is :
  1. A
    3x + 2y = 6xy
  2. B
    3x + 2y = 6
  3. C
    2x + 3y = xy
  4. D
    3x + 2y = xy
View written solutionFree

Correct answer: D

  1. Let the line cut the xxx-axis at P(a,0)P(a,0)P(a,0) and the yyy-axis at Q(0,b)Q(0,b)Q(0,b), where a≠0a\neq 0a=0, b≠0b\neq 0b=0.

  2. Since the rectangle OPRQOPRQOPRQ is completed with O=(0,0)O=(0,0)O=(0,0), P=(a,0)P=(a,0)P=(a,0), Q=(0,b)Q=(0,b)Q=(0,b), the fourth vertex is R=(a,b).R=(a,b).R=(a,b). So if R=(x,y)R=(x,y)R=(x,y), then a=x,b=y.a=x,\quad b=y.a=x,b=y.

  3. The line joining P(a,0)P(a,0)P(a,0) and Q(0,b)Q(0,b)Q(0,b) has intercept form Xa+Yb=1.\frac{X}{a}+\frac{Y}{b}=1.aX​+bY​=1. It passes through the fixed point (2,3)(2,3)(2,3), so 2a+3b=1.\frac{2}{a}+\frac{3}{b}=1.a2​+b3​=1.

  4. Now substitute a=xa=xa=x and b=yb=yb=y: 2x+3y=1.\frac{2}{x}+\frac{3}{y}=1.x2​+y3​=1. Multiplying by xyxyxy, 2y+3x=xy.2y+3x=xy.2y+3x=xy. Rearranging, 3x+2y=xy.3x+2y=xy.3x+2y=xy.

  5. Therefore, the locus of RRR is 3x+2y=xy.\boxed{3x+2y=xy}. 3x+2y=xy​.

  6. Checking options:

  • A: 3x+2y=6xy3x+2y=6xy3x+2y=6xy ❌
  • B: 3x+2y=63x+2y=63x+2y=6 ❌
  • C: 2x+3y=xy2x+3y=xy2x+3y=xy ❌
  • D: 3x+2y=xy3x+2y=xy3x+2y=xy ✅

Hence the correct option is D.

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