Mathematics
Grade 8
15 min
Area
Area
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1
Introduction & Learning Objectives
Learning Objectives
Calculate the area of basic two-dimensional shapes (squares, rectangles, triangles, parallelograms, trapezoids).
Determine the area of circles and semicircles using the appropriate formula.
Decompose complex polygons into simpler shapes to find their total area.
Apply the Pythagorean theorem to find missing dimensions required for area calculations.
Solve real-world problems involving area calculations.
Understand and correctly use appropriate square units for area measurements.
Ever wondered how much paint you need for a wall or how much grass seed for your lawn? 🤔 It all comes down to understanding 'area'!
In this lesson, you'll learn to measure the amount of two-dimensional space inside various shapes, from simple squares to complex fi...
2
Key Concepts & Vocabulary
TermDefinitionExample
AreaThe amount of two-dimensional space a shape or surface covers, measured in square units.A square with sides of 5 cm has an area of 25 square centimeters ($25 \text{ cm}^2$). This means 25 squares, each 1 cm by 1 cm, would fit inside it.
Base (of a polygon)Any side of a polygon chosen as the bottom, used in conjunction with height for area calculations.In a triangle, the base is often the side it 'rests' on, but any side can be chosen as the base. For a rectangle, either the length or width can be considered the base.
Height (of a polygon)The perpendicular distance from the base to the opposite vertex or side.For a triangle, it's the perpendicular distance from a vertex to the opposite base. For a parallelogram, it's the perpendicular distance...
3
Core Formulas
Area of a Rectangle/Square
$A = l \times w$ (for rectangle) or $A = s^2$ (for square)
To find the area of a rectangle, multiply its length ($l$) by its width ($w$). For a square, multiply the side length ($s$) by itself.
Area of a Triangle
$A = \frac{1}{2} \times b \times h$
To find the area of a triangle, multiply half of its base ($b$) by its perpendicular height ($h$). The height must be perpendicular to the chosen base.
Area of a Trapezoid
$A = \frac{1}{2} \times (b_1 + b_2) \times h$
To find the area of a trapezoid, add the lengths of the two parallel bases ($b_1$ and $b_2$), multiply by the perpendicular height ($h$), and then divide by two.
Area of a Circle
$A = \pi r^2$
To find the area of a circle, multiply pi ($\pi \approx 3.14159$) by the square of...
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Challenging
A circular park has a radius of 50 meters. A walkway with a width of 5 meters is built around the park. What is the area of the walkway itself? Leave your answer in terms of π.
A.25π m²
B.275π m²
C.500π m²
D.525π m²
Challenging
The area of an isosceles triangle is 48 cm². Its base is 12 cm. The height of the triangle forms two right triangles. What is the length of one of the two equal slanted sides (the hypotenuse of the right triangle)?
A.6 cm
B.8 cm
C.10 cm
D.14 cm
Challenging
A contractor is tiling an L-shaped room. The room can be seen as a 12 ft by 18 ft rectangle with a 5 ft by 8 ft rectangular corner removed. If the tiles cost $4 per square foot, what is the total cost to tile the room?
A.$704
B.$864
C.$160
D.$1024
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