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← JEE Main 2026 · 8 Apr · Shift 2
MathematicsInteger+4 / -1Question 24 of 75

JEE Main 2026 · 8 Apr · Shift 2, Mathematics question 24

Consider the circle C:x2+y2−6x−8y−11=0C:x^2+y^2-6x-8y-11=0. Let a variable chord AB of the circle C subtend a right angle at the origin. If the locus of the foot of the perpendicular drawn from the origin on the chord AB is the circle x2+y2−αx−βy−γ=0x^2+y^2-\alpha x-\beta y-\gamma=0, then α+β+2γ\alpha+\beta+2\gamma is equal to ________.

Answer and worked solution

Official answer: 18

Chord with foot (h, k). Its equation is hx+ky=phx+ky=p, with p=h2+k2p=h^2+k^2.

Right angle at O. Homogenise the circle with hx+kyp=1\tfrac{hx+ky}p=1; the x2x^2 and y2y^2 coefficients must add to zero:
2−6h+8kp−11p=0 ⇒ 2(h2+k2)−6h−8k−11=0.2-\frac{6h+8k}p-\frac{11}p=0\ \Rightarrow\ 2(h^2+k^2)-6h-8k-11=0.

Locus. x2+y2−3x−4y−112=0x^2+y^2-3x-4y-\tfrac{11}2=0: α=3\alpha=3, β=4\beta=4, γ=112\gamma=\tfrac{11}2.

Answer. α+β+2γ=18\alpha+\beta+2\gamma=18.