Sample Question 23:

A regular octagon $ABCDEFGH$ has an area of one square unit. What is the area of the rectangle $ABEF$?

$\textbf{(A) } 1 - \frac{\sqrt{2}}{2} \qquad\textbf{(B) } \frac{\sqrt{2}}{4} \qquad\textbf{(C) } \sqrt{2} - 1 \qquad\textbf{(D) } \frac{1}{2} \qquad\textbf{(E) } \frac{1+\sqrt{2}}{4}$

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Answer Keys

Question 23: D

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Solutions

Question 23
Step 1: The area of a regular octagon is given by the formula $\frac{ap}{2}=1$, where $a$ is the apothem and $p$ is the perimeter.

Step 2: This octagon's side length is $\frac{p}{8}$ and the apothem is $2a$.

Step 3: The area of the rectangle $ABEF$ is given by the formula $\frac{p}{8} \times 2a = \frac{2ap}{8} = \frac{ap}{4}$.

Step 4: From steps 1 and 3, we can observe that the area of the rectangle is half the area of the octagon.

Step 5: Since the area of the octagon is one unit square, the area of the rectangle $ABEF$ is $\frac{1}{2}$ unit square.

Therefore, the answer is $\textbf{(D)}\ \frac{1}{2}$.