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Lesson 4-2: Area & Perimeter of Triangles

Scenario: Architectural Design - Design triangular structures using area and perimeter calculations!

Duration: 55-70 minutesScenario: Architectural Design

Learning Objectives

  • Calculate area of triangles using A = ½ × base × height
  • Calculate perimeter of triangles by adding all three sides
  • Identify base and height in different triangle orientations
  • Apply triangle calculations to architectural design problems

Architectural Design Problem

Triangular Roof Design

You're designing a triangular roof for a small building. The roof has a base of 12 meters and a height of 8 meters. You need to calculate the area for roofing materials and the perimeter for the trim.

Questions:
1. How much roofing material do you need? (Area)
2. How much trim do you need for the edges? (Perimeter)

12 m (base)
8 m (height)

Visual representation of the triangular roof

Step-by-Step Solution

Step 1: Calculate the area (roofing material needed)

Area = ½ × base × height
Area = ½ × 12 m × 8 m
Area = ½ × 96 m² = 48 m²

Step 2: Calculate the perimeter (trim needed)

To find perimeter, we need all three sides.
We know: base = 12 m, height = 8 m
Using Pythagorean theorem for the two equal sides:
Side = √(6² + 8²) = √(36 + 64) = √100 = 10 m
Perimeter = 10 + 10 + 12 = 32 m

Answer: You need 48 m² of roofing material and 32 m of trim.

Triangle Formulas

Area Formula

A = ½ × b × h

Area = ½ × base × height
Units: square units (m², ft², etc.)

Key Point: The height must be perpendicular to the base!

Perimeter Formula

P = a + b + c

Perimeter = side₁ + side₂ + side₃
Units: linear units (m, ft, etc.)

Key Point: Add all three sides together!

Different Triangle Types

Right Triangle

One angle is 90°
Height is one of the legs

Isosceles Triangle

Two equal sides
Height splits base in half

Scalene Triangle

All sides different
Height must be measured

Practice Problems

Problem 1

A triangular garden plot has a base of 15 meters and a height of 10 meters. Calculate the area and perimeter (assuming it's an isosceles triangle).

Your solution:

Problem 2

A triangular flag has sides of 5 cm, 12 cm, and 13 cm. Find the area and perimeter of the flag.

Your solution: