Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Circle question

2011 · Shift 2 · Q25
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Advanced
  3. /Mathematics
  4. /Circle
  5. /2011 · Shift 2 · Q25

Circle question

2011 · Shift 2 · Q25

JEE AdvancedMathematicsCircleNumerical+2 / −1
The straight line 2x - 3y = 1 divides the circular region x2 + y2 ≤ 6{x^2}\, + \,{y^2}\, \le \,6x2+y2≤6 into two parts. If S={(2, 34), (52, 34), (14− 14), (18, 14)}S = \left\{ {\left( {2,\,{3 \over 4}} \right),\,\left( {{5 \over 2},\,{3 \over 4}} \right),\,\left( {{1 \over 4} - \,{1 \over 4}} \right),\,\left( {{1 \over 8},\,{1 \over 4}} \right)} \right\}S={(2,43​),(25​,43​),(41​−41​),(81​,41​)} then the number of points (s) in S lying inside the smaller part is
Numerical answer
View written solutionFree

Correct answer: 2

  1. Circle and dividing line

The circular region is x2+y2≤6,x^2+y^2\le 6,x2+y2≤6, so the circle has center (0,0)(0,0)(0,0) and radius 6\sqrt{6}6​.

The line is 2x−3y=1.2x-3y=1.2x−3y=1. This line divides the disk into two parts. Since the center (0,0)(0,0)(0,0) does not lie on the line, the smaller part is the side of the line away from the center.

Let us check which side contains the center: 2(0)−3(0)−1=−1<0.2(0)-3(0)-1=-1<0.2(0)−3(0)−1=−1<0. So the center lies in the region 2x−3y−1<0.2x-3y-1<0.2x−3y−1<0. Hence the smaller part is the other side: 2x−3y−1>0.2x-3y-1>0.2x−3y−1>0.

Also, since all given points must lie inside the circular region as well, we will check both:

  • x2+y2≤6x^2+y^2\le 6x2+y2≤6
  • 2x−3y−1>02x-3y-1>02x−3y−1>0

  1. Given set of points

The set is S={(2,34),(52,34),(14,−14),(18,14)}.S=\left\{\left(2,\frac34\right),\left(\frac52,\frac34\right),\left(\frac14,-\frac14\right),\left(\frac18,\frac14\right)\right\}.S={(2,43​),(25​,43​),(41​,−41​),(81​,41​)}.


  1. Test each point

(i) Point (2,34)\left(2,\frac34\right)(2,43​)

Check circle: x2+y2=22+(34)2=4+916=7316<6x^2+y^2=2^2+\left(\frac34\right)^2=4+\frac{9}{16}=\frac{73}{16}<6x2+y2=22+(43​)2=4+169​=1673​<6 since 6=9616.6=\frac{96}{16}.6=1696​. So it lies inside the disk.

Check line side: 2x−3y−1=2(2)−3(34)−1=4−94−1=3−94=34>0.2x-3y-1=2(2)-3\left(\frac34\right)-1=4-\frac94-1=3-\frac94=\frac34>0.2x−3y−1=2(2)−3(43​)−1=4−49​−1=3−49​=43​>0. So this point lies in the smaller part.


(ii) Point (52,34)\left(\frac52,\frac34\right)(25​,43​)

Check circle: x2+y2=(52)2+(34)2=254+916=10016+916=10916.x^2+y^2=\left(\frac52\right)^2+\left(\frac34\right)^2=\frac{25}{4}+\frac{9}{16}=\frac{100}{16}+\frac{9}{16}=\frac{109}{16}.x2+y2=(25​)2+(43​)2=425​+169​=16100​+169​=16109​. Now, 6=9616,6=\frac{96}{16},6=1696​, so 10916>6.\frac{109}{16}>6.16109​>6. Hence this point is outside the circular region, so it cannot lie inside either part.


(iii) Point (14,−14)\left(\frac14,-\frac14\right)(41​,−41​)

Check circle: x2+y2=(14)2+(−14)2=116+116=18<6.x^2+y^2=\left(\frac14\right)^2+\left(-\frac14\right)^2=\frac1{16}+\frac1{16}=\frac18<6.x2+y2=(41​)2+(−41​)2=161​+161​=81​<6. So it lies inside the disk.

Check line side: 2x−3y−1=2(14)−3(−14)−1=12+34−1=54−1=14>0.2x-3y-1=2\left(\frac14\right)-3\left(-\frac14\right)-1=\frac12+\frac34-1=\frac54-1=\frac14>0.2x−3y−1=2(41​)−3(−41​)−1=21​+43​−1=45​−1=41​>0. So this point also lies in the smaller part.


(iv) Point (18,14)\left(\frac18,\frac14\right)(81​,41​)

Check circle: x2+y2=(18)2+(14)2=164+116=164+464=564<6.x^2+y^2=\left(\frac18\right)^2+\left(\frac14\right)^2=\frac1{64}+\frac1{16}=\frac1{64}+\frac4{64}=\frac5{64}<6.x2+y2=(81​)2+(41​)2=641​+161​=641​+644​=645​<6. So it lies inside the disk.

Check line side: 2x−3y−1=2(18)−3(14)−1=14−34−1=−12−1=−32<0.2x-3y-1=2\left(\frac18\right)-3\left(\frac14\right)-1=\frac14-\frac34-1=-\frac12-1=-\frac32<0.2x−3y−1=2(81​)−3(41​)−1=41​−43​−1=−21​−1=−23​<0. So this point lies in the larger part, not the smaller part.


  1. Count points in the smaller part

Points in the smaller part are: (2,34),(14,−14).\left(2,\frac34\right),\quad \left(\frac14,-\frac14\right).(2,43​),(41​,−41​).

Thus, the number of points is 2.\boxed{2}.2​.


  1. Comparison with stored answer

Stored correct answer = 222.

Our derived answer is also 222, so they agree.

PreviousNext

More from Circle

  • Tangents drawn from the point P (1, 8) to the circle x2+y2−6x−4y−11=0 touch the circle at the points A and B. The equation of the cirumcircle of the triangle PAB is2009 · MCQ
  • The centres of two circles C1​ and C2​ each of unit radius are at a distance of 6 units from each other. Let P be the mid point of the line segement joining the centres of C1​ and C2​ and C a circle touching circles C1​…2009 · Numerical
  • A circle C of radius 1 is inscribed in an equilateral triangle PQR. The points of contact of C with the sides PQ, QR, RP are D, E, F, respectively. The line PQ is given by the equation 3​x+y−6=0 and the point D is (233​​,23​)…2008 · MCQ
  • A circle C of radius 1 is inscribed in an equilateral triangle PQR. The points of contact of C with the sides PQ, QR, RP are D, E, F, respectively. The line PQ is given by the equation 3​x+y−6=0 and the point D is (233​​,23​)…2008 · MCQ
  • A circle C of radius 1 is inscribed in an equilateral triangle PQR. The points of contact of C with the sides PQ, QR, RP are D, E, F, respectively. The line PQ is given by the equation 3​x+y−6=0 and the point D is (233​​,23​)…2008 · MCQ
  • Consider L1​:2x+3y+p−3=0L2​:2x+3y+p+3=0 where p is a real number, and C:x2+y2+6x−10y+30=0 STATEMENT-1 : If line L1​ is a…2008 · MCQ
  • Tangents are drawn from the point (17, 7) to the circle x2+y2=169. Statement 1 : The tangents are mutually perpendicular. Statement 2 : The locus of the points from which mutually perpendicular tangents can be drawn to the given circle…2007 · MCQ
  • Let the straight line y=2x touch a circle with center (0,α),α>0, and radius r at a point A1​. Let B1​ be the point on the circle such that the line segment A1​B1​ is a diameter of the circle. Let α+r=5+5​… Includes table2024 · MCQ