ISI question

[RichaS]

The answer is d, can someone please explain how, as i am getting 'a' as the answer

[Abhitesh]

Already explained elsewhere.

[Daffodils]

can u share the link or explain? I tried finding the link but to no avail

[Abhitesh]

If we try to maximise/ minimise the function through calculus we get A as answer. BUT that is local maximum/minimum.
There are values of f(x) with given constraints that are greater/lesser that the local values. And as you move towards infinity you will get an ever increasing value of f(x).