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KVPY2016MathematicsApplication of Derivatives

Let f ( x ) be a non-negative differentiable function on [0, ) such that f (0)=0 and f ( x ) 2 f ( x ) for all x >0 . Then, on [0, )

Options

  1. Af ( x ) is always a constant function
  2. Bf ( x ) is strictly increasing
  3. Cf ( x ) is strictly decreasing
  4. Df ^ ( x ) changes sign

Correct answer

A. f ( x ) is always a constant function

Step-by-step solution

f ^ ( x ) 2 f ( x ) f ^ ( x ) e ^ -2 x 2 f ( x ) e ^ -2 x d dx ( f ( x ) e ^ -2 n ) 0 ~g ( x )= f ( x ) e ^ -2 x is non-Increasing function x 0 ~g ( x ) g (0) f ( x ) e ^ -2 x f (0) e ⁻⁰ f ( x ) e ^ -2 x 0 f ( x ) 0 but given f ( x ) is not negative f ( x )=0 Constant function

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