Week 4 and 5 – Jss 2 Second Term Basic Technology Lesson Notes

Week 4&5; area of plane figure

Area of Plane Shapes

Area is the size of a surface!Learn more about Area, or try the Area Calculator.

	TriangleArea = ½ × b × hb = baseh = vertical height			SquareArea = a2a = length of side
	RectangleArea = w × hw = widthh = height			ParallelogramArea = b × hb = baseh = vertical height
	Trapezoid (US)Trapezium (UK)Area = ½(a+b) × hh = vertical height			Circle Area = π × r2 Circumference = 2 × π × rr = radius
	EllipseArea = πab			SectorArea = ½ × r2 × θ r = radiusθ = angle in radians
Note: h is at right angles to b:

Example: What is the area of this rectangle?

The formula is:
Area = w × hw = widthh = height
We know w = 5 and h = 3, so:
Area = 5 × 3 = 15

Example: What is the area of this circle?

Radius = r = 3

Example: What is the area of this triangle?

Height = h = 12
Base = b = 20
Area = ½ × b × h = ½ × 20 × 12 = 120
 
 A harder example:

Example: Sam cuts grass at $0.10 per square meter

How much does Sam earn cutting this area:

Let’s break the area into two parts:

Part A is a square:
Area of A = a² = 20m × 20m = 400m²
Part B is a triangle. Viewed sideways it has a base of 20m and a height of 14m.
Area of B = ½b × h = ½ × 20m × 14m = 140m²
So the total area is:
Area = Area of A + Area of B = 400m² + 140m² = 540m²
 
 Sam earns $0.10 per square meter
Sam earns = $0.10 × 540m² = $54
Assignment

• Construct a rectangle equal to the area of a given triangle