dse 2011 q23

[VARSHA G]

the closest point on parabola y=1/4x^2 from a given point (o,b) on the vertical axis , with b>0 is the origin if and only if
A. b<3
B. b>3
C.b<2
D.b>2



how do we do it !?

[divyas]

guys plz help wid this one!!
m also not getting this

[Khagesh]

well u shld u derivative test for d options....dats wat i'd use....

or

Take any general point wid d given option set whichever gives d least distance frm origin rather than any oder point is d ans

[Ankit Agrawal]

The value of b must be the smallest, i.ie. it should fall in that option where it takes the smallest value.
b takes the smallest value, among the given options, when it is less than 2.

You can apply this logic:

For eg., we choose option (a) b < 3. Then we are saying that when b is more than 3, say 4, then the nearest point on the parabola is (0,0). But at the same time we are saying that if b < 3, say 2, then the nearest point on the parabola is not (0,0) but some thing else, which is completely obscure and meaningless.

Hence, the smallest number would be the answer.