$\{x \in \mathbb{R} \mid \frac{\sqrt{|x|^2 - 2|x| - 8}}{\log(2 - x - x^2)}\}$ is a real number.

$\{x \in \mathbb{R} \mid \frac{\sqrt{|x|^2 - 2|x| - 8}}{\log(2 - x - x^2)}\}$ is a real number.
  1. (-,-4]U[4,)
  2. ϕ
  3. -1,2
  4. (-,-4]-1,2[4,)

Solution

Let

fx=x2-2x-8log2-x-x2

fx=x2-2x-8log-x2-x+1

log-x2-x+1 is defined for 

-x2-x+1>0

x2+x-1<0

x--1+52x--1-52<0

x-1-52,-1+52

x-1.61,0.61   ....i

And,

x2-2x-80

Put x=t

t2-2t-80

t+2t-40

t(-,-2][4,)

x(-,-2][4,)

But x0 xR, so

x[4,)

x(-,-4][4,)   ....ii

But i  ii is ϕ, so option B is correct.

Asked in: AP EAMCET 2022 (04 Jul Shift 2)

Practice more Functions questions on Aicharya