## Info

Step 1 You know that the area is y the base times the height. A = y(18 m X 7 m)

Step 2 Multiply y by the product of 18 X 7. Multiply the units.2

The area is 63 m2.

Practice Problem Find the area of a triangle with a base of 27 cm and a height of 17 cm.

### Circumference of a Circle The diameter

(d) of a circle is the distance across the circle through its center, and the radius (r) is the distance from the center to any point on the circle. The radius is half of the diameter. The distance around the circle is called the circumference (C). The formula for finding the circumference is:

The circumference divided by the diameter is always equal to 3.1415926... This nonter-minating and nonrepeating number is represented by the Greek letter j (pi). An approximation often used for j is 3.14.

Example 1 Find the circumference of a circle with a radius of 3 m.

Step 1 You know the formula for the circumference is 2 times the radius times J. C = 2j(3)

Step 2 Multiply 2 times the radius. C = 6 J

The circumference is 19 m.

Example 2 Find the circumference of a circle with a diameter of 24.0 cm.

Step 1 You know the formula for the circumference is the diameter times j. C = j(24.0)

Step 2 Multiply the diameter by J. C = 75.4 cm

The circumference is 75.4 cm.

Practice Problem Find the circumference of a circle with a radius of 19 cm.

Area of a Circle The formula for the area of a circle is: A = jr2

Example 1 Find the area of a circle with a radius of 4.0 cm.

Step 2 Find the square of the radius. A = 16j

Step 3 Multiply the square of the radius by J. A = 50 cm2

The area of the circle is 50 cm2.

Example 2 Find the area of a circle with a radius of 225 m.

Step 2 Find the square of the radius. A = 50625J

Step 3 Multiply the square of the radius by J. A = 158962.5

The area of the circle is 158,962 m2.

Example 3 Find the area of a circle whose diameter is 20.0 mm.

Step 1 You know the formula for the area of a circle is the square of the radius times j, and that the radius is half of the diameter.