Math Problem Statement

The radii of the circle drawn in the right triangle and circled on it are equal to 2 cm and 5 cm, respectively. Find the sides of the triangle.

Solution

To solve this, we need to analyze the relationship between the radii of the incircle and the circumcircle of a right triangle, which are given as r=2cmr = 2 \, \text{cm} (radius of the incircle) and R=5cmR = 5 \, \text{cm} (radius of the circumcircle).

Properties and Relationships:

  1. For a right triangle:

    • The circumradius RR is half the hypotenuse:
      R=c2R = \frac{c}{2} where cc is the hypotenuse.
    • The inradius rr is given by:
      r=a+bc2r = \frac{a + b - c}{2} where aa and bb are the other two sides of the triangle.
  2. Using the Pythagorean theorem:
    c2=a2+b2c^2 = a^2 + b^2


Step 1: Hypotenuse from RR

Given R=5cmR = 5 \, \text{cm}, the hypotenuse cc is: c=2R=25=10cm.c = 2R = 2 \cdot 5 = 10 \, \text{cm}.


Step 2: Relation involving rr

Using the formula for the inradius: r=a+bc2.r = \frac{a + b - c}{2}. Substituting r=2cmr = 2 \, \text{cm} and c=10cmc = 10 \, \text{cm}: 2=a+b102.2 = \frac{a + b - 10}{2}. Simplifying: a+b=14.a + b = 14.


Step 3: Solve for aa and bb

Using the Pythagorean theorem c2=a2+b2c^2 = a^2 + b^2 with c=10c = 10: 100=a2+b2.100 = a^2 + b^2. We now solve the system of equations:

  1. a+b=14a + b = 14
  2. a2+b2=100a^2 + b^2 = 100

Let b=14ab = 14 - a. Substitute into the second equation: a2+(14a)2=100.a^2 + (14 - a)^2 = 100. Expand and simplify: a2+19628a+a2=100,a^2 + 196 - 28a + a^2 = 100, 2a228a+96=0.2a^2 - 28a + 96 = 0. Divide through by 2: a214a+48=0.a^2 - 14a + 48 = 0. Factorize: (a8)(a6)=0.(a - 8)(a - 6) = 0. Thus: a=8ora=6.a = 8 \quad \text{or} \quad a = 6.

If a=8a = 8, then b=148=6b = 14 - 8 = 6.
If a=6a = 6, then b=146=8b = 14 - 6 = 8.


Final Answer:

The sides of the triangle are: a=6cm,b=8cm,c=10cm.a = 6 \, \text{cm}, \, b = 8 \, \text{cm}, \, c = 10 \, \text{cm}.

Would you like more details or explanations on any step?


Follow-up Questions:

  1. Why is the circumradius RR always half the hypotenuse in a right triangle?
  2. What are some applications of the inradius and circumradius in geometry?
  3. How does the relationship a+bc=2ra + b - c = 2r generalize to non-right triangles?
  4. Can you derive the formula for the inradius using the area of the triangle?
  5. How does the Pythagorean theorem ensure the solution is unique?

Tip: When solving systems of equations, substitution is often a powerful method for reducing variables efficiently.

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Math Problem Analysis

Mathematical Concepts

Geometry
Right Triangles
Circle Properties
Inradius and Circumradius Relationships

Formulas

Circumradius of a right triangle: R = c / 2
Inradius of a right triangle: r = (a + b - c) / 2
Pythagorean theorem: c^2 = a^2 + b^2

Theorems

Pythagorean Theorem
Properties of Incircle and Circumcircle

Suitable Grade Level

Grades 9-12