1. **State the problem:** We have a right triangle ABC with a right angle at A. The hypotenuse BC is 36 cm, and the segment from A to the point where the inscribed circle touches the triangle is 10 cm. We need to find the radius of the inscribed circle.
2. **Recall the formula for the inradius (radius of the inscribed circle) of a right triangle:**
$$r = \frac{a + b - c}{2}$$
where $a$ and $b$ are the legs of the right triangle, and $c$ is the hypotenuse.
3. **Identify known values:**
- Hypotenuse $c = 36$ cm
- The segment from $A$ to the tangent point of the circle is 10 cm. This segment corresponds to $s - a$, where $s$ is the semiperimeter and $a$ is one leg.
4. **Use the tangent length property:** The tangent length from a vertex to the point of tangency with the incircle equals $s -$ the side adjacent to that vertex.
Given the tangent length from $A$ is 10 cm, then:
$$10 = s - a$$
5. **Express the semiperimeter:**
$$s = \frac{a + b + c}{2}$$
So,
$$10 = \frac{a + b + 36}{2} - a = \frac{a + b + 36 - 2a}{2} = \frac{b + 36 - a}{2}$$
Multiply both sides by 2:
$$20 = b + 36 - a$$
Rearranged:
$$b - a = -16$$
6. **Use the Pythagorean theorem:**
$$a^2 + b^2 = 36^2 = 1296$$
7. **From step 5, express $b$ in terms of $a$:**
$$b = a - 16$$
8. **Substitute into Pythagorean theorem:**
$$a^2 + (a - 16)^2 = 1296$$
Expand:
$$a^2 + a^2 - 32a + 256 = 1296$$
Combine like terms:
$$2a^2 - 32a + 256 = 1296$$
Subtract 1296:
$$2a^2 - 32a + 256 - 1296 = 0$$
$$2a^2 - 32a - 1040 = 0$$
Divide entire equation by 2:
$$a^2 - 16a - 520 = 0$$
9. **Solve quadratic equation:**
$$a = \frac{16 \pm \sqrt{(-16)^2 - 4 \times 1 \times (-520)}}{2} = \frac{16 \pm \sqrt{256 + 2080}}{2} = \frac{16 \pm \sqrt{2336}}{2}$$
Calculate $\sqrt{2336} \approx 48.34$:
$$a = \frac{16 \pm 48.34}{2}$$
Two solutions:
- $$a = \frac{16 + 48.34}{2} = 32.17$$
- $$a = \frac{16 - 48.34}{2} = -16.17$$ (discard negative length)
10. **Find $b$:**
$$b = a - 16 = 32.17 - 16 = 16.17$$
11. **Calculate semiperimeter $s$:**
$$s = \frac{a + b + c}{2} = \frac{32.17 + 16.17 + 36}{2} = \frac{84.34}{2} = 42.17$$
12. **Calculate inradius $r$:**
$$r = s - c = 42.17 - 36 = 6.17$$
Or use the formula:
$$r = \frac{a + b - c}{2} = \frac{32.17 + 16.17 - 36}{2} = \frac{12.34}{2} = 6.17$$
**Final answer:** The radius of the inscribed circle is approximately **6.17 cm**.
Triangle Inradius 943437
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