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

2025 · 4 Apr · Shift 1 · Q46
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 Main
  3. /Mathematics
  4. /Circle
  5. /2025 · 4 Apr · Shift 1 · Q46

Circle question

2025 · 4 Apr · Shift 1 · Q46

JEE MainMathematicsCircleNumerical+4 / −1
Let CCC be the circle x2+(y−1)2=2,E1x^2+(y-1)^2=2, E_1x2+(y−1)2=2,E1​ and E2E_2E2​ be two ellipses whose centres lie at the origin and major axes lie on x -axis and y -axis respectively. Let the straight line x+y=3x+y=3x+y=3 touch the curves C,E1C, E_1C,E1​ and E2E_2E2​ at P(x1,y1),Q(x2,y2)P\left(x_1, y_1\right), Q\left(x_2, y_2\right)P(x1​,y1​),Q(x2​,y2​) and R(x3,y3)R\left(x_3, y_3\right)R(x3​,y3​) respectively. Given that PPP is the mid point of the line segment QRQ RQR and PQ=223P Q=\frac{2 \sqrt{2}}{3}PQ=322​​, the value of 9(x1y1+x2y2+x3y3)9\left(x_1 y_1+x_2 y_2+x_3 y_3\right)9(x1​y1​+x2​y2​+x3​y3​) is equal to ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 46

  1. Find the tangency point PPP of the line with the circle

The circle is x2+(y−1)2=2x^2+(y-1)^2=2x2+(y−1)2=2 with centre OC=(0,1)O_C=(0,1)OC​=(0,1) and radius r=2r=\sqrt2r=2​.

The line is x+y=3.x+y=3.x+y=3. Its distance from (0,1)(0,1)(0,1) is ∣0+1−3∣12+12=22=2,\frac{|0+1-3|}{\sqrt{1^2+1^2}}=\frac{2}{\sqrt2}=\sqrt2,12+12​∣0+1−3∣​=2​2​=2​, so it is indeed tangent.

For a tangent point, the radius is perpendicular to the tangent. Since the line has slope −1-1−1, the radius has slope 111. So the radius through (0,1)(0,1)(0,1) is y=x+1.y=x+1.y=x+1. Intersect with x+y=3x+y=3x+y=3:

y=2.y=2.y=2. Hence P=(x1,y1)=(1,2).P=(x_1,y_1)=(1,2).P=(x1​,y1​)=(1,2).


  1. Use midpoint condition to get RRR from QQQ

Given PPP is midpoint of QRQRQR, P=(x2+x32,y2+y32)=(1,2).P=\left(\frac{x_2+x_3}{2},\frac{y_2+y_3}{2}\right)=(1,2).P=(2x2​+x3​​,2y2​+y3​​)=(1,2). Thus x2+x3=2,y2+y3=4.x_2+x_3=2,\qquad y_2+y_3=4.x2​+x3​=2,y2​+y3​=4.

Also Q,RQ,RQ,R lie on the same line x+y=3x+y=3x+y=3, and PPP lies on that line. So they are collinear.

Given PQ=223.PQ=\frac{2\sqrt2}{3}.PQ=322​​. Since PPP is midpoint of QRQRQR, we also have PR=PQ=223.PR=PQ=\frac{2\sqrt2}{3}.PR=PQ=322​​.

The direction vector of the line x+y=3x+y=3x+y=3 is (1,−1)(1,-1)(1,−1), whose unit vector is 12(1,−1).\frac{1}{\sqrt2}(1,-1).2​1​(1,−1). So moving distance 223\frac{2\sqrt2}{3}322​​ along this line changes coordinates by 223⋅12(1,−1)=(23,−23).\frac{2\sqrt2}{3}\cdot \frac{1}{\sqrt2}(1,-1)=\left(\frac23,-\frac23\right).322​​⋅2​1​(1,−1)=(32​,−32​). Hence the two points at that distance from P=(1,2)P=(1,2)P=(1,2) on the line are (1+23,2−23)=(53,43),\left(1+\frac23,2-\frac23\right)=\left(\frac53,\frac43\right),(1+32​,2−32​)=(35​,34​), (1−23,2+23)=(13,83).\left(1-\frac23,2+\frac23\right)=\left(\frac13,\frac83\right).(1−32​,2+32​)=(31​,38​). So QQQ and RRR are these two points in some order.


  1. Identify which point belongs to which ellipse

Ellipse E1E_1E1​

Its centre is origin and major axis is along the xxx-axis, so its equation is of the form x2a2+y2b2=1,a>b>0.\frac{x^2}{a^2}+\frac{y^2}{b^2}=1,\qquad a>b>0.a2x2​+b2y2​=1,a>b>0. For the tangent line x+y=3x+y=3x+y=3, write it as y=−x+3.y=-x+3.y=−x+3. A line y=mx+cy=mx+cy=mx+c is tangent to this ellipse iff c2=a2m2+b2.c^2=a^2m^2+b^2.c2=a2m2+b2. Here m=−1,c=3m=-1,c=3m=−1,c=3, hence 9=a2+b2.9=a^2+b^2.9=a2+b2.

For ellipse x2a2+y2b2=1\frac{x^2}{a^2}+\frac{y^2}{b^2}=1a2x2​+b2y2​=1, tangent at (x0,y0)(x_0,y_0)(x0​,y0​) is xx0a2+yy0b2=1.\frac{xx_0}{a^2}+\frac{yy_0}{b^2}=1.a2xx0​​+b2yy0​​=1. Comparing with x+y=3x+y=3x+y=3, i.e. x+y3=1,\frac{x+y}{3}=1,3x+y​=1, we get x0a2=13,y0b2=13,\frac{x_0}{a^2}=\frac13,\qquad \frac{y_0}{b^2}=\frac13,a2x0​​=31​,b2y0​​=31​, so x0=a23,y0=b23.x_0=\frac{a^2}{3},\qquad y_0=\frac{b^2}{3}.x0​=3a2​,y0​=3b2​. Thus x0+y0=a2+b23=3.x_0+y_0=\frac{a^2+b^2}{3}=3.x0​+y0​=3a2+b2​=3. So the tangency point on such an ellipse is (a23,b23),\left(\frac{a^2}{3},\frac{b^2}{3}\right),(3a2​,3b2​), with first coordinate larger than second because a>ba>ba>b.

Among our two candidate points, only (53,43)\left(\frac53,\frac43\right)(35​,34​) has x>yx>yx>y. Therefore Q=(53,43).Q=\left(\frac53,\frac43\right).Q=(35​,34​).

Ellipse E2E_2E2​

Its centre is origin and major axis is along the yyy-axis, so its tangency point must have y>xy>xy>x. Thus R=(13,83).R=\left(\frac13,\frac83\right).R=(31​,38​).


  1. Compute x1y1+x2y2+x3y3x_1y_1+x_2y_2+x_3y_3x1​y1​+x2​y2​+x3​y3​

Now x1y1=1⋅2=2,x_1y_1=1\cdot 2=2,x1​y1​=1⋅2=2, x2y2=53⋅43=209,x_2y_2=\frac53\cdot \frac43=\frac{20}{9},x2​y2​=35​⋅34​=920​, x3y3=13⋅83=89.x_3y_3=\frac13\cdot \frac83=\frac{8}{9}.x3​y3​=31​⋅38​=98​. Therefore x1y1+x2y2+x3y3=2+209+89=2+289=469.x_1y_1+x_2y_2+x_3y_3=2+\frac{20}{9}+\frac{8}{9}=2+\frac{28}{9}=\frac{46}{9}.x1​y1​+x2​y2​+x3​y3​=2+920​+98​=2+928​=946​. Hence 9(x1y1+x2y2+x3y3)=46.9(x_1y_1+x_2y_2+x_3y_3)=46.9(x1​y1​+x2​y2​+x3​y3​)=46.


  1. Final answer

The required integer is 46.\boxed{46}.46​.

This matches the stored correct answer.

PreviousNext

More from Circle

  • Let C1​ be the circle in the third quadrant of radius 3 , that touches both coordinate axes. Let C2​ be the circle with centre (1,3) that touches C1​ externally at the point (α,β). If (β−α)2=nm​…2025 · MCQ
  • A circle C of radius 2 lies in the second quadrant and touches both the coordinate axes. Let r be the radius of a circle that has centre at the point (2,5) and intersects the circle C at exactly two points. If the set of all possible…2025 · MCQ
  • Let the circle C touch the line x−y+1=0, have the centre on the positive x-axis, and cut off a chord of length 13​4​ along the line −3x+2y=1. Let H be the hyperbola α2x2​−β2y2​=1,…2025 · Numerical
  • Let circle C be the image of x2+y2−2x+4y−4=0 in the line 2x−3y+5=0 and A be the point on C such that OA is parallel to x-axis and A lies on the right hand side of the centre O of C. If B(α,β), with β<4…2025 · MCQ
  • Let the equation of the circle, which touches x-axis at the point (a,0),a>0 and cuts off an intercept of length b on y−axis be x2+y2−αx+βy+γ=0. If the circle lies below x−axis, then the ordered pair…2025 · MCQ
  • Let the line x+y=1 meet the circle x2+y2=4 at the points A and B. If the line perpendicular to AB and passing through the mid-point of the chord AB intersects the circle at C and D, then the area of the quadrilateral ABCD is equal to :2025 · MCQ
  • Let a circle C pass through the points (4, 2) and (0, 2), and its centre lie on 3x + 2y + 2 = 0. Then the length of the chord, of the circle C, whose mid-point is (1, 2), is:2025 · MCQ
  • Let C:x2+y2=4 and C′:x2+y2−4λx+9=0 be two circles. If the set of all values of λ so that the circles C and C intersect at two distinct points, is $\mathrm{R}-[\mathrm{a},…2024 · MCQ