11Q59 If the line x-2=0 is the directrix of the parabola y2-kx+4=0 then one of the values of k is
a) 4+4√2
b) 4-4√2
c) 4
d) -4
Your Answer: (a)
Correct Answer: (c)
Score: -1
Explaination :
y2=k(x-4/k)
Y2=4(k/4)X
X=x-4/k
X=k/4 is the directrix
x-4/k=k/4 gives 2-4/k=k/4
8k-16=k2
k=4
also X=-k/4 is one of the directrix
2-4/k=-k/4
8k-16=-k2
k=-4±4√2
according to the solution
answer should be E
no option exists[2]
