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← JEE Main 2022 · 27 Jul · Shift 2
MathematicsInteger+4 / -1Question 29 of 90

JEE Main 2022 · 27 Jul · Shift 2, Mathematics question 29

A common tangent T to the curves C1:x24+y29=1C_1:\dfrac{x^2}4+\dfrac{y^2}9=1 and C2:x242−y2143=1C_2:\dfrac{x^2}{42}-\dfrac{y^2}{143}=1 does not pass through the fourth quadrant. If T touches C1C_1 at (x1,y1)(x_1,y_1) and C2C_2 at (x2,y2)(x_2,y_2), then ∣2x1+x2∣|2x_1+x_2| is equal to ______.

Answer and worked solution

Official answer: 20

Common tangent. 4m2+9=42m2−1434m^2+9=42m^2-143 gives m2=4m^2=4 and c2=25c^2=25. Avoiding the fourth quadrant: y=2x+5y=2x+5.

Contacts. x1=−4⋅25x_1=-\frac{4\cdot2}5 and x2=−42⋅25x_2=-\frac{42\cdot2}5, so ∣2x1+x2∣=20|2x_1+x_2|=20.

Answer: 20