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McGraw Hill Glencoe Algebra 1, 2012

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McGraw Hill Glencoe Algebra 1, 2012 View details

8. Area

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Exercise 10 Page p28

The area of a circle is the product of the radius squared and $π .$

$78.5 in^{2}$

The area of a circle is the product of the radius squared and

π .

A = π r^{2}

From the figure, we know that the radius of a circle is

5

inches. Let's substitute this value into the formula.

A = π r^{2}

$r = 5$

A = π (5)^{2}

Calculate power

A = π (25)

CommutativePropMult

Commutative Property of Multiplication

A = 25 π

Use a calculator

A = 78.53981 \dots

Round to $1$ decimal place(s)

A \approx 78.5

The area of the circle is approximately

78.5

square inches.

Extra

Formula for the Area

We know that the area is the number of square units needed to cover a surface. Since there are so many figures with different shapes, we can have a formula for the area of each figure. Let's see some examples!

Sometimes, we will come across with complex figures without a formula for the area. In that cases, we can follow the next steps.

Break the shape down into simpler figures.
Find the area of each smaller figure. We can use the known formulas for the area.
Add the areas of each smaller figure. The total area will be the area of the complex figure.

For those of you who are interested in learning more about the area of other figures, you can read more about them on the following pages.

Area of a Kite
Area of a Rhombus
Area of a Trapezoid