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Algebra Difficulty 3.5 AMC 10/12 Find the answer

Consider the sets A={xx1>2}A=\{x \mid |x-1| > 2\} and B={xx(x5)<0}B=\{x \mid x(x-5) < 0\}. Find the intersection ABA \cap B.

A number or a short expression. Spacing and $ signs are ignored.

Solution

First, let's solve the inequality for set AA. We understand that the absolute value x1|x-1| being greater than 2 means that the quantity inside the absolute value must be either greater than 2 or less than -2.

For x1>2x-1 > 2, we get:
\begin{align*}
x-1 &> 2 \\
x &> 3
\end{align*}

For x13 or x<1}x-1 3 \text{ or } x < -1\}.

Next, let's analyze set BB. The inequality x(x5)<0x(x-5) < 0 implies that the product of xx and (x5)(x-5) is negative. This means that xx and (x5)(x-5) have opposite signs. Based on the zero product property, the solution will be between the two roots of the quadratic equation, which are x=0x = 0 and x=5x = 5.

As a result, B={x0<x<5}B=\{x \mid 0 < x < 5\}.

Now we need to determine the intersection ABA \cap B, which consists of elements that are common to both sets AA and BB. The set AA includes numbers greater than 3 and less than -1, and the set BB includes numbers between 0 and 5.

Therefore, the intersection ABA \cap B will only include numbers that are between 3 and 5, because that is the region where the conditions of both sets AA and BB are satisfied simultaneously.

The solution is:
AB={x3<x<5} A \cap B = \{x \mid 3 < x < 5\}

We can highlight the final answer as:
AB={x3<x<5} \boxed{ A \cap B = \{x \mid 3 < x < 5\} }

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.