Lesson 10: Geometry: Area & Perimeter
Area measures how much surface a shape covers (square units). Perimeter measures the total length around a shape. These calculations appear in architecture, art, agriculture, and engineering.
Key Concepts
Rectangle & Square
Perimeter = 2l + 2w (or 4s for a square). Area = l × w (or s² for a square). Units matter: if length is in feet, area is in square feet (ft²).
Triangle
Perimeter = sum of all three sides. Area = ½ × base × height. The height must be perpendicular (at a right angle) to the base — it's not always a side of the triangle.
Circle
Circumference (perimeter) = 2πr = πd. Area = πr². π ≈ 3.14159. Remember: r is radius (center to edge), d is diameter (all the way across) = 2r.
Composite Shapes
Break complex shapes into simpler pieces. Find each area separately. Add them up (or subtract for cutouts). Example: an L-shape = two rectangles.
🔬 Interactive Lab: Geometry: Area & Perimeter Lab
✅ Check Your Understanding
1. What is the area of a rectangle with length 8 and width 5?
2. The area of a triangle with base 10 and height 6 is:
3. The area of a circle uses which formula?