If x+y=k is a normal to the parabola y2=12x then k is
A
3
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B
9
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C
−9
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D
−3
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Solution
The correct option is B9 Equation of normal to the parabola y2=4ax is given by y=mx−2am−am3..(1), (Here a=3) Now since line (1) and y=−x+k represent same line ⇒m=−1∴k=−2am−am3=−2(3)(−1)+3(1)=9