Math Problem Statement

A triangle ABC is drawn to circumscribe a circle of radius 4 cm such that the segments BD and DC into which BC is divided by the point of contact D are of lengths 8 cm and 6 cm respectively .Find the sides AB and AC. Solve this without heron's formula .

Solution

To solve this problem without using Heron's formula, we can make use of properties of a triangle inscribed around a circle (an incircle). Here's the step-by-step solution:

Step 1: Understanding the Given Data and Setting Up Variables

  • We have a triangle ABCABC circumscribing a circle with radius r=4r = 4 cm.
  • The incircle touches side BCBC at point DD, dividing BCBC into segments BD=8BD = 8 cm and DC=6DC = 6 cm.

Let:

  • AB=cAB = c
  • AC=bAC = b
  • BC=aBC = a

Thus, a=BD+DC=8+6=14a = BD + DC = 8 + 6 = 14 cm.

Step 2: Apply the Incircle Property

The incircle divides each side into two segments such that each segment is equal to the semiperimeter (ss) minus the length of the opposite side.

So we know:

  • BD=scBD = s - c
  • DC=sbDC = s - b

Step 3: Calculate the Semiperimeter ss

The semiperimeter ss of the triangle is given by: s=a+b+c2s = \frac{a + b + c}{2}

Since BD=8BD = 8 and DC=6DC = 6, we have: sc=8andsb=6s - c = 8 \quad \text{and} \quad s - b = 6

Step 4: Express bb and cc in Terms of ss

Rearrange the equations to find bb and cc in terms of ss: c=s8c = s - 8 b=s6b = s - 6

Step 5: Use the Area Formula for an Incircle

The area AA of a triangle with an incircle is given by: A=srA = s \cdot r Since r=4r = 4 cm, we have: A=4sA = 4s

Step 6: Calculate the Area in Terms of aa, bb, and cc

The area AA can also be expressed using the base aa and the altitude (height) to that base, which we calculate via: A=12×a×hA = \frac{1}{2} \times a \times h where hh is the height from AA to BCBC.

Equating both expressions for the area AA: 4s=12×a×h4s = \frac{1}{2} \times a \times h

Since we are not given hh, we proceed with finding the values for ss, bb, and cc directly by substituting values and solving accordingly.

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Math Problem Analysis

Mathematical Concepts

Geometry
Incircle of a Triangle
Semiperimeter
Area of a Triangle

Formulas

Semiperimeter formula s = (a + b + c) / 2
Area of a triangle using incircle A = s * r

Theorems

Incircle and Semiperimeter Theorem

Suitable Grade Level

Grades 9-11