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If $$A = \{x \in R : |x-2| > 1\}$$, $$B = \{x \in R : \sqrt{x^2 - 3} > 1\}$$, $$C = \{x \in R : |x-4| \geq 2\}$$ and $$Z$$ is the set of all integers, then the number of subsets of the set $$(A \cap B \cap C)^c \cap Z$$ is _________.
Correct Answer: 256
We begin by translating each set description into interval form on the real number line.
For set $$A$$ we have the condition $$|x-2|>1$$. The definition of absolute value gives the equivalence
$$|x-2|>1 \;\Longrightarrow\; x-2<-1 \;\text{ or }\; x-2>1.$$
Simplifying each inequality,
$$x<1 \;\text{ or }\; x>3.$$
Hence
$$A=(-\infty,1)\cup(3,\infty).$$
For set $$B$$ the requirement is $$\sqrt{x^{2}-3}>1.$$ Because the square-root function is non-negative, we square both sides, knowing the direction of the inequality will not change:
$$\bigl(\sqrt{x^{2}-3}\bigr)^{2}>1^{2}\quad\Longrightarrow\quad x^{2}-3>1.$$
This rearranges to
$$x^{2}>4\quad\Longrightarrow\quad |x|>2.$$
Therefore
$$B=(-\infty,-2)\cup(2,\infty).$$
For set $$C$$ we are given $$|x-4|\ge 2$$. Using the same absolute-value definition,
$$|x-4|\ge 2 \;\Longrightarrow\; x-4\le-2 \;\text{ or }\; x-4\ge 2,$$
which simplifies to
$$x\le2 \;\text{ or }\; x\ge6.$$
Thus
$$C=(-\infty,2]\cup[6,\infty).$$
Now we find the intersection $$A\cap B$$. Writing the two interval unions together,
$$A=(-\infty,1)\cup(3,\infty),\qquad B=(-\infty,-2)\cup(2,\infty).$$
On the left half-line $$(-\infty,1)$$, the part common with $$B$$ is the portion further restricted by $$x<-2$$, giving $$(-\infty,-2).$$ On the right half-line $$(3,\infty)$$, every point already satisfies $$x>2$$, so the whole interval $$(3,\infty)$$ survives. Consequently
$$A\cap B=(-\infty,-2)\cup(3,\infty).$$
Next we intersect this result with $$C$$:
$$C=(-\infty,2]\cup[6,\infty).$$
The interval $$(-\infty,-2)$$ of $$A\cap B$$ obviously lies inside $$(-\infty,2]$$ of $$C$$, so it remains unchanged. The interval $$(3,\infty)$$ meets $$C$$ only where $$x\ge6$$, giving $$[6,\infty).$$ Therefore
$$A\cap B\cap C=(-\infty,-2)\cup[6,\infty).$$
We now form the complement of this set inside $$\mathbb R$$. Using the fact that the complement of a union is the union of complements, we remove both pieces from the real line:
$$\bigl(A\cap B\cap C\bigr)^{c}=\mathbb R\setminus\bigl((-\infty,-2)\cup[6,\infty)\bigr)=\,[ -2,6 ).$$
Here $$-2$$ is included because it was not in the intersection (the first interval was open at $$-2$$), while $$6$$ is excluded because it was contained in the intersection (the second interval was closed at $$6$$).
To finish, we intersect with $$Z$$, the set of all integers. The integers lying in $$[-2,6)$$ are
$$\{-2,-1,0,1,2,3,4,5\}.$$
We count their number:
$$n=8.$$
The question asks for the number of subsets of this finite set. A fundamental result of set theory states that a set with $$n$$ elements has $$2^{n}$$ distinct subsets (including the empty set and the set itself). Substituting $$n=8$$, we get
$$2^{8}=256.$$
So, the answer is $$256$$.
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