A pedestrian crossing sign is the shape of a regular pentagon. The radius of the sign is 15 in. What is the apothem of the pentagon? Round your answer to 2 decimal places.

1 answer

To find the apothem of a regular pentagon, we can use the formula that relates the radius (\( R \)) and the apothem (\( a \)):

\[ a = R \cdot \cos\left(\frac{\pi}{n}\right) \]

where \( n \) is the number of sides of the polygon. For a pentagon, \( n = 5 \).

Given:

  • Radius \( R = 15 \) inches
  • Number of sides \( n = 5 \)

Now, we calculate the angle:

\[ \frac{\pi}{n} = \frac{\pi}{5} \]

Next, we compute \( \cos\left(\frac{\pi}{5}\right) \):

\[ \cos\left(\frac{\pi}{5}\right) \approx 0.8090 \]

Now, we can find the apothem:

\[ a = 15 \cdot \cos\left(\frac{\pi}{5}\right) \approx 15 \cdot 0.8090 \approx 12.135 \]

Finally, rounding to two decimal places, we have:

\[ a \approx 12.14 \text{ inches} \]

Thus, the apothem of the pentagon is approximately 12.14 inches.