Math Problem Statement

A triangle is to be drawn with sides that are integer lengths in centimeters, and a total perimeter of 12 cm. How many different (non-congruent) triangles can be drawn?

Solution

The problem asks for how many different (non-congruent) triangles can be drawn with sides that are integers, where the perimeter is 12 cm.

Solution Outline:

We are looking for integer side lengths aa, bb, and cc such that:

  1. a+b+c=12a + b + c = 12 (since the perimeter is 12 cm)
  2. The sides must satisfy the triangle inequality:
    • a+b>ca + b > c
    • a+c>ba + c > b
    • b+c>ab + c > a

Step-by-Step Solution:

Given the perimeter is 12, we can write the equation:

a+b+c=12a + b + c = 12 From this, c=12abc = 12 - a - b. Now, substitute this into the triangle inequality conditions:

  1. a+b>ca+b>12ab2a+2b>12a+b>6a + b > c \Rightarrow a + b > 12 - a - b \Rightarrow 2a + 2b > 12 \Rightarrow a + b > 6
  2. a+c>ba+(12ab)>b12b>bb<6a + c > b \Rightarrow a + (12 - a - b) > b \Rightarrow 12 - b > b \Rightarrow b < 6
  3. Similarly, b+c>ab+(12ab)>a12a>aa<6b + c > a \Rightarrow b + (12 - a - b) > a \Rightarrow 12 - a > a \Rightarrow a < 6

So, we need to find pairs of integers aa, bb, and c=12abc = 12 - a - b such that a+b+c=12a + b + c = 12, and a+b>6a + b > 6.

We now check all possible combinations of aa, bb, and cc under these conditions:

aabbccTriangle Inequality Satisfied?
156Yes
246Yes
255Yes
336Yes
345Yes
444Yes

Thus, there are 5 different (non-congruent) triangles.

Answer:

The correct answer is 5.

Would you like further details or explanations?

Related Questions:

  1. How can we determine the number of non-congruent triangles for a different perimeter?
  2. What are the triangle inequality conditions?
  3. Can two triangles with the same perimeter and different side lengths be congruent?
  4. What are the properties of integer-sided triangles?
  5. How does the triangle inequality relate to different types of triangles?

Tip: Always check the triangle inequality after finding the side lengths to ensure a valid triangle!

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Math Problem Analysis

Mathematical Concepts

Geometry
Triangle Inequality
Integer-sided Triangles

Formulas

Perimeter of triangle: a + b + c
Triangle Inequality: a + b > c, a + c > b, b + c > a

Theorems

Triangle Inequality Theorem

Suitable Grade Level

Grades 9-12