The function, f x = 3 x - 7 x 2 3 ,   x ∈ R , is increasing for all x lying in

The function, fx=3x-7x23, xR, is increasing for all x lying in
  1. -,01415,
  2. -,037,
  3. -,1415
  4. -,-14150,

Solution

fx=3x-7x23

For fx is increasing f'x>0.

Differentiate fx

f'x=3x23+3x-723x13

f'x=9x+23x-73x13

f'x=15x-143x13

Now f'x>0  15x-143x13>0

x-, 01415, 

Asked in: JEE Main 2020 (03 Sep Shift 1)

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