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Hyperbola question

2024 · 30 Jan · Shift 2 · Q43
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  5. /2024 · 30 Jan · Shift 2 · Q43

Hyperbola question

2024 · 30 Jan · Shift 2 · Q43

JEE MainMathematicsHyperbolaMCQ+4 / −1
Let PPP be a point on the hyperbola H:x29−y24=1H: \frac{x^2}{9}-\frac{y^2}{4}=1H:9x2​−4y2​=1, in the first quadrant such that the area of triangle formed by PPP and the two foci of HHH is 2132 \sqrt{13}213​. Then, the square of the distance of PPP from the origin is
  1. A
    26
  2. B
    22
  3. C
    20
  4. D
    18
View written solutionFree

Correct answer: B

  1. Write the hyperbola and its foci

    Given H:x29−y24=1H: \frac{x^2}{9}-\frac{y^2}{4}=1H:9x2​−4y2​=1

    This is of the form x2a2−y2b2=1\frac{x^2}{a^2}-\frac{y^2}{b^2}=1a2x2​−b2y2​=1 with a2=9,b2=4a^2=9,\quad b^2=4a2=9,b2=4

    For such a hyperbola, c2=a2+b2=9+4=13  ⟹  c=13c^2=a^2+b^2=9+4=13 \implies c=\sqrt{13}c2=a2+b2=9+4=13⟹c=13​

    Hence the two foci are F1=(13,0),F2=(−13,0)F_1=(\sqrt{13},0),\qquad F_2=(-\sqrt{13},0)F1​=(13​,0),F2​=(−13​,0)

  2. Use the area condition

    Let P=(x,y)P=(x,y)P=(x,y) be a point on the hyperbola in the first quadrant, so x>0,y>0x>0,y>0x>0,y>0.

    The triangle is formed by PPP and the two foci. The base is the segment joining the foci: F1F2=213F_1F_2 = 2\sqrt{13}F1​F2​=213​

    Since the foci lie on the xxx-axis, the perpendicular distance of PPP from the line F1F2F_1F_2F1​F2​ is simply yyy.

    Therefore, area of triangle PF1F2PF_1F_2PF1​F2​ is 12⋅213⋅y=13 y\frac{1}{2}\cdot 2\sqrt{13}\cdot y = \sqrt{13}\,y21​⋅213​⋅y=13​y

    Given area is 2132\sqrt{13}213​, so 13 y=213  ⟹  y=2\sqrt{13}\,y = 2\sqrt{13} \implies y=213​y=213​⟹y=2

  3. Use the fact that PPP lies on the hyperbola

    Substitute y=2y=2y=2 into x29−y24=1\frac{x^2}{9}-\frac{y^2}{4}=19x2​−4y2​=1

    x29−44=1\frac{x^2}{9}-\frac{4}{4}=19x2​−44​=1 x29−1=1\frac{x^2}{9}-1=19x2​−1=1 x29=2\frac{x^2}{9}=29x2​=2 x2=18x^2=18x2=18

  4. Find the square of the distance from the origin

    The square of the distance of PPP from the origin is OP2=x2+y2=18+4=22OP^2=x^2+y^2=18+4=22OP2=x2+y2=18+4=22

  5. Check options

    222222 corresponds to Option B.

  6. Compare with stored answer

    Stored correct answer is B, which matches our result.

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