If x + y = k is normal to y2 = 12 x, then k is :
(A) 3 (B) 9
(C) –9 (D) –3

slope of parabola at any point is :

dy/dx = 12/2y

slope of line is -1,

as line is normal, (-1)*(12/2y) = -1

y = 6 and so x is 3

so eqn of line is x+y=9

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Ramesh
IIT Kgp - 05 batch