Functions Warmup 1 (Domain)

Algebra Level 2

Find the domain of the following real function:

f ( x ) = 4 3 x ln x \large f(x)=\frac{\sqrt{4-|3-x|}}{\ln x}

( 0 , 1 ) ( 1 , 7 ] (0,1) \cup (1,7] [ 1 , 1 ) ( 1 , 7 ) [-1,1) \cup (1,7) [ 1 , 7 ] [-1,7] ( 0 , 7 ] (0,7]

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1 solution

Aris M
Mar 11, 2020

A couple of days have gone by so I will post the solution here.
For f f to be well defined, the following restrictions on x have to exist:

1) The denominator cannot be zero. Therefore: ln x 0 ln x l n 1 x 1 \ln x \neq 0 \Leftrightarrow \ln x \neq ln 1 \Leftrightarrow x \neq 1
2) The argument of the logarithm must be strictly positive. Therefore: x > 0 x>0
3) The expression under the radical must be nonnegative. Therefore: 4 3 x 0 3 x 4 4 3 x 4 7 x 1 1 x 7 4 - |3-x|\geqslant 0\Leftrightarrow |3-x|\leqslant 4\Leftrightarrow -4\leqslant 3-x \leqslant 4\Leftrightarrow -7\leqslant -x \leqslant 1\Leftrightarrow -1\leqslant x \leqslant 7

By combining the three restrictions above we get x ( 0 , 1 ) ( 1 , 7 ] \boxed{x \in (0,1)\cup (1,7]} which is our final answer.

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