Q31 / 90 · JEE Main 2023 (01 Feb Shift 1) · Mathematics

Let fx=2x+tan-1x and gx=loge1+x2+x, x∈0,3. Then

  • A
    There exists x∈0,3 such that f'x<g'x
  • Correct answer
    B
    max fx>max gx
  • C
    There exist 0<x1<x2<3 such that fx<gx, ∀x∈x1,x2
  • D
    min f'x=1+max g'x

Solution

Given:

fx=2x+tan-1x

⇒f'x=2+11+x2

And,

gx=ln1+x2+x

⇒g'x=11+x2

Now,

0≤x≤3

⇒0≤x2≤9

⇒1≤1+x2≤10

So,

110≤11+x2≤1

⇒2+110≤2+11+x2≤3

⇒2+110≤f'x≤3

⇒2110≤f'x≤3

And,

110≤g'x≤1

So, min f'x=2110≠1+max g'x

Option 4 is incorrect

From above,

g'x<f'x∀x∈0,3

Option 1 is incorrect.

Since, f'x and g'x are both positive so fx and gx both are increasing

So,

maxfx at x=3 is 6+tan-13

maxgx at x=3 is ln3+10 

And, 6+tan-13>ln3+10 

Option 2 is correct

Hence, the correct answer is option: 'B'.

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