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Hyperbola question

2021 · 25 Jul · Shift 1 · Q26
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  5. /2021 · 25 Jul · Shift 1 · Q26

Hyperbola question

2021 · 25 Jul · Shift 1 · Q26

JEE MainMathematicsHyperbolaMCQ+4 / −1
The locus of the centroid of the triangle formed by any point P on the hyperbola 16x2−9y2+32x+36y−164=016{x^2} - 9{y^2} + 32x + 36y - 164 = 016x2−9y2+32x+36y−164=0, and its foci is :
  1. A
    16x2−9y2+32x+36y−36=016{x^2} - 9{y^2} + 32x + 36y - 36 = 016x2−9y2+32x+36y−36=0
  2. B
    9x2−16y2+36x+32y−144=09{x^2} - 16{y^2} + 36x + 32y - 144 = 09x2−16y2+36x+32y−144=0
  3. C
    16x2−9y2+32x+36y−144=016{x^2} - 9{y^2} + 32x + 36y - 144 = 016x2−9y2+32x+36y−144=0
  4. D
    9x2−16y2+36x+32y−36=09{x^2} - 16{y^2} + 36x + 32y - 36 = 09x2−16y2+36x+32y−36=0
View written solutionFree

Correct answer: A

  1. Write the hyperbola in standard form

Given: 16x2−9y2+32x+36y−164=016x^2-9y^2+32x+36y-164=016x2−9y2+32x+36y−164=0

Group terms and complete squares: 16(x2+2x)−9(y2−4y)−164=016(x^2+2x)-9(y^2-4y)-164=016(x2+2x)−9(y2−4y)−164=0

16[(x+1)2−1]−9[(y−2)2−4]−164=016[(x+1)^2-1]-9[(y-2)^2-4]-164=016[(x+1)2−1]−9[(y−2)2−4]−164=0

16(x+1)2−16−9(y−2)2+36−164=016(x+1)^2-16-9(y-2)^2+36-164=016(x+1)2−16−9(y−2)2+36−164=0

16(x+1)2−9(y−2)2−144=016(x+1)^2-9(y-2)^2-144=016(x+1)2−9(y−2)2−144=0

So, 16(x+1)2−9(y−2)2=14416(x+1)^2-9(y-2)^2=14416(x+1)2−9(y−2)2=144

Divide by 144144144: (x+1)29−(y−2)216=1\frac{(x+1)^2}{9}-\frac{(y-2)^2}{16}=19(x+1)2​−16(y−2)2​=1

Hence the hyperbola has:

  • center C(−1,2)C(-1,2)C(−1,2)
  • a2=9,  b2=16a^2=9,\; b^2=16a2=9,b2=16
  • c2=a2+b2=25⇒c=5c^2=a^2+b^2=25 \Rightarrow c=5c2=a2+b2=25⇒c=5

Therefore the foci are: F1=(−1−5,2)=(−6,2),F2=(−1+5,2)=(4,2)F_1=(-1-5,2)=(-6,2), \qquad F_2=(-1+5,2)=(4,2)F1​=(−1−5,2)=(−6,2),F2​=(−1+5,2)=(4,2)


  1. Take any point PPP on the hyperbola

Let P=(x,y)P=(x,y)P=(x,y) be any point on the given hyperbola.

The triangle is formed by the three points P,F1,F2P, F_1, F_2P,F1​,F2​.

Its centroid G(X,Y)G(X,Y)G(X,Y) is X=x+(−6)+43=x−23,X=\frac{x+(-6)+4}{3}=\frac{x-2}{3},X=3x+(−6)+4​=3x−2​, Y=y+2+23=y+43.Y=\frac{y+2+2}{3}=\frac{y+4}{3}.Y=3y+2+2​=3y+4​.

So, x=3X+2,y=3Y−4.x=3X+2, \qquad y=3Y-4.x=3X+2,y=3Y−4.


  1. Substitute into the hyperbola equation

Original equation: 16x2−9y2+32x+36y−164=016x^2-9y^2+32x+36y-164=016x2−9y2+32x+36y−164=0

Substitute x=3X+2x=3X+2x=3X+2, y=3Y−4y=3Y-4y=3Y−4:

16(3X+2)2−9(3Y−4)2+32(3X+2)+36(3Y−4)−164=016(3X+2)^2-9(3Y-4)^2+32(3X+2)+36(3Y-4)-164=016(3X+2)2−9(3Y−4)2+32(3X+2)+36(3Y−4)−164=0

Now expand:

(3X+2)2=9X2+12X+4(3X+2)^2=9X^2+12X+4(3X+2)2=9X2+12X+4 16(3X+2)2=144X2+192X+6416(3X+2)^2=144X^2+192X+6416(3X+2)2=144X2+192X+64

(3Y−4)2=9Y2−24Y+16(3Y-4)^2=9Y^2-24Y+16(3Y−4)2=9Y2−24Y+16 −9(3Y−4)2=−81Y2+216Y−144-9(3Y-4)^2=-81Y^2+216Y-144−9(3Y−4)2=−81Y2+216Y−144

Also, 32(3X+2)=96X+6432(3X+2)=96X+6432(3X+2)=96X+64 36(3Y−4)=108Y−14436(3Y-4)=108Y-14436(3Y−4)=108Y−144

Adding all terms: 144X2+192X+64−81Y2+216Y−144+96X+64+108Y−144−164=0144X^2+192X+64-81Y^2+216Y-144+96X+64+108Y-144-164=0144X2+192X+64−81Y2+216Y−144+96X+64+108Y−144−164=0

144X2−81Y2+288X+324Y−324=0144X^2-81Y^2+288X+324Y-324=0144X2−81Y2+288X+324Y−324=0

Divide by 999: 16X2−9Y2+32X+36Y−36=016X^2-9Y^2+32X+36Y-36=016X2−9Y2+32X+36Y−36=0

Thus the locus of the centroid is 16x2−9y2+32x+36y−36=016x^2-9y^2+32x+36y-36=016x2−9y2+32x+36y−36=0

(where we rename X,YX,YX,Y back to x,yx,yx,y).


  1. Match with the options

This is exactly:

Option A: 16x2−9y2+32x+36y−36=016x^2-9y^2+32x+36y-36=016x2−9y2+32x+36y−36=0


  1. Conclusion

The required locus is: 16x2−9y2+32x+36y−36=0\boxed{16x^2-9y^2+32x+36y-36=0}16x2−9y2+32x+36y−36=0​

So the correct option is A.

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