Quantitative Aptitude Ques 26

Question: For any real number x, the maximum value of $ 4-6x-x^{2} $

Options:

A) 4

B) 7

C) 9

D) 13

Show Answer

Answer:

Correct Answer: D

Solution:

  • Let the given equation be represented as $ f(x)=4-6x-x^{2} $
    Now, differentiating above function w.r.t x, we get
    $ f’(x)=-,6-2x $ For value of x put $ f’(x)=0 $ $ -,6-2x=0 $

$ \therefore $ $ x=-,3 $ For maximum value, we take $ f’(x) $ $ f’(x)=-,2 $ Since, value of $ f’(x) $ is negative. So, $ f(x) $ is maximum at $ x=-,3. $ Putting in $ x=-,3 $ in $ f(x), $ we get $ f(-,3)=4-(6)(-,3)-{{(-,3)}^{2}} $ $ =4+18-9=13 $ So, the maximum value of $ =4-6x-x^{2} $ is 13.