Differential Equations 1 Question 21

21. Which of the following is true?

(a) 0<f(x)<

(b) 12<f(x)<12

(c) 14<f(x)<1

(d) <f(x)<0

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Solution:

  1. Here, f(x)2f(x)+f(x)ex

f(x)exf(x)exf(x)ex+f(x)ex0

ddxf(x)exddxf(x)ex1

ddxf(x)exf(x)ex1

d2dx2exf(x)1,x[0,1]

φ(x)=exf(x) is concave function.

f(0)=f(1)=0φ(0)=0=f(1)φ(x)<0exf(x)<0f(x)<0



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