1. **State the problem:** We have a regular pentagon with an inscribed circle (incircle) of radius $r=5$ cm. We need to find the area of the pentagon outside the circle, i.e., $\text{Area}_{\text{pentagon}} - \text{Area}_{\text{circle}}$.
2. **Recall formulas:**
- Area of circle: $\pi r^2$
- For a regular pentagon with side length $a$ and apothem $r$, area is $\frac{1}{2} \times \text{perimeter} \times r = \frac{1}{2} \times 5a \times r$
3. **Find side length $a$ of the pentagon:**
The apothem $r$ relates to side length $a$ by
$$r = \frac{a}{2 \tan(\pi/5)}$$
Rearranged:
$$a = 2r \tan(\pi/5)$$
Calculate $\tan(\pi/5)$:
$$\tan(36^\circ) \approx 0.7265425$$
So,
$$a = 2 \times 5 \times 0.7265425 = 7.265425$$ cm
4. **Calculate area of pentagon:**
$$\text{Area}_{\text{pentagon}} = \frac{1}{2} \times 5a \times r = \frac{1}{2} \times 5 \times 7.265425 \times 5 = \frac{1}{2} \times 5 \times 7.265425 \times 5 = 90.8178$$ cm$^2$
5. **Calculate area of circle:**
$$\text{Area}_{\text{circle}} = \pi r^2 = \pi \times 5^2 = 25\pi \approx 78.5398$$ cm$^2$
6. **Calculate area outside the circle:**
$$\text{Area}_{\text{outside}} = 90.8178 - 78.5398 = 12.278$$ cm$^2$
7. **Round to 2 decimal places:**
$$12.28$$ cm$^2$
**Final answer:** The area of the pentagon outside the circle is approximately $12.28$ cm$^2$.
Pentagon Circle Area
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