Area of a Circle
Grade 8 math lesson on the area of a circle using the formula A = pi times r squared. Students learn to identify the radius, apply the pi r squared formula, and calculate circle areas with both exact answers in terms of pi and decimal approximations.
Key Concepts
New Concept The area of a circle is $\pi$ times the area of a square on its radius. This relationship is expressed with the formula: $$A = \pi r^2$$ What’s next This card is just the start. Next, you’ll tackle worked examples for finding the area of full circles and even parts of circles, called sectors.
Common Questions
What is the formula for the area of a circle?
The area of a circle = pi times radius squared, written as A = pi r squared. The radius is the distance from the center to the edge of the circle.
How do you find the area of a circle if you know the diameter?
If you know the diameter, divide it by 2 to find the radius, then apply the formula A = pi r squared. For example, a circle with diameter 10 has radius 5, so area = pi times 25 = 25pi square units.
What is the difference between area and circumference of a circle?
Area measures the space inside the circle (in square units) using A = pi r squared. Circumference measures the distance around the circle (in linear units) using C = 2 pi r or C = pi d.
Why do we use pi in the area formula?
Pi (approximately 3.14159) is the ratio of a circle circumference to its diameter. It appears in area and circumference formulas because circles have this constant relationship built into their geometry.