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JEE Main 20254 AprilMorning Shift
Exam
JEE Main
Year
2025
Date
4 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Ellipse

JEE Main 2025 · 4 April · Morning Shift · Mathematics · Ellipse

Let C be the circle x^2+(y-1)^2=2, E_1 and E_2 be two ellipses...

Let C be the circle x2+(y−1)2=2,E1\mathrm{x}^2+(\mathrm{y}-1)^2=2, \mathrm{E}_1 and E2\mathrm{E}_2 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=3 touch the curves CC, E1E_1 and E2E_2 at PP\left(x_1, y_1\right), Q(x2,y2)Q\left(x_2, y_2\right) and $R(x3,y3)R\left(x_3, y_3\right) respectively. Given that PP is the mid-point of the line segment QRQ R and PQ=223P Q=\frac{2 \sqrt{2}}{3}, the value of 99\left(x_1 y_1+x_2 y_2+x_3 y_3\right)$ is equal to ______ .

Correct answer

0

Step-by-step solution

Let E1:x2a2+y2 b2=1,(a>b)\mathrm{E}_1: \frac{\mathrm{x}^2}{\mathrm{a}^2}+\frac{\mathrm{y}^2}{\mathrm{~b}^2}=1,(\mathrm{a} \gt \mathrm{b})
E2:x2c2+y2 d2=1,(c<d)\mathrm{E}_2: \frac{\mathrm{x}^2}{\mathrm{c}^2}+\frac{\mathrm{y}^2}{\mathrm{~d}^2}=1,(\mathrm{c} \lt \mathrm{d})
C:x2+(y−1)2=2C: x^2+(y-1)^2=2
Equation of tangent at P(x1,y1)\mathrm{P}\left(\mathrm{x}_1, \mathrm{y}_1\right)
xx1+y(y1−1)=(y1+1)\mathrm{xx}_1+\mathrm{y}\left(\mathrm{y}_1-1\right)=\left(\mathrm{y}_1+1\right)
comparing with x+y=3\mathrm{x}+\mathrm{y}=3 we get P(1,2)\mathrm{P}(1,2)
∵\because Now parametric equation of x+y=3x+y=3
(x−1)(−12)=(y−2)(12)=±223(∵PQ=223)\frac{(\mathrm{x}-1)}{\left(\frac{-1}{\sqrt{2}}\right)}=\frac{(\mathrm{y}-2)}{\left(\frac{1}{\sqrt{2}}\right)}= \pm \frac{2 \sqrt{2}}{3} \quad\left(\because \mathrm{PQ}=\frac{2 \sqrt{2}}{3}\right)
On solving we get Q(53,43),R(13,83)\mathrm{Q}\left(\frac{5}{3}, \frac{4}{3}\right), \mathrm{R}\left(\frac{1}{3}, \frac{8}{3}\right)
So, 9(x1y1+x2y2+x3y3)9\left(\mathrm{x}_1 \mathrm{y}_1+\mathrm{x}_2 \mathrm{y}_2+\mathrm{x}_3 \mathrm{y}_3\right)
<br/>9(2+53×43+13×83)⇒46<br/>\begin{aligned}<br/>& 9\left(2+\frac{5}{3} \times \frac{4}{3}+\frac{1}{3} \times \frac{8}{3}\right) \\ & \Rightarrow 46<br/>\end{aligned}
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