Question ID: #694
Let $A=\{x:|x^{2}-10|\le6\}$ and $B=\{x:|x-2|>1\}$. Then
- (1) $A\cup B=(-\infty,1]\cup(2,\infty)$
- (2) $A-B=[2,3)$
- (3) $A\cap B=[-4,-2]\cup[3,4]$
- (4) $B-A=(-\infty,-4)\cup(-2,1)\cup(4,\infty)$
Solution:
First, solve the inequality for set $A$:
$$|x^{2}-10|\le6$$
$$-6 \le x^{2}-10 \le 6$$
$$4 \le x^{2} \le 16$$
Taking the square root, we get two disjoint intervals:
$$x \in [-4, -2] \cup [2, 4]$$
So, $A = [-4, -2] \cup [2, 4]$.
Next, solve the inequality for set $B$:
$$|x-2| > 1$$
$$x-2 > 1 \quad \text{or} \quad x-2 < -1$$
$$x > 3 \quad \text{or} \quad x < 1$$
So, $B = (-\infty, 1) \cup (3, \infty)$.
Now, calculate $B – A$ (elements present in $B$ but not in $A$):
$B – A = ((-\infty, 1) \cup (3, \infty)) – ([-4, -2] \cup [2, 4])$
Subtracting the interval $[-4, -2]$ from $(-\infty, 1)$:
The remaining part is $(-\infty, -4) \cup (-2, 1)$.
Subtracting the interval $[2, 4]$ from $(3, \infty)$:
The intersection is $(3, 4]$. Removing this from $(3, \infty)$ leaves $(4, \infty)$.
Combining the remaining parts:
$$B – A = (-\infty, -4) \cup (-2, 1) \cup (4, \infty)$$
Ans. (4)
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