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Step-5

Title: Area of circle

Grade: 7-a Lesson: S1-L2

Explanation:

Step	Type	Explanation	Answer
1	Problem	The area of a circle is \$81 picm^2\$. Find the radius.
2	Formula:	Area of a circle.	A = \$pi r^2\$
3	Step	Substitute \$81 \pi\$ for A	\$81 \pi\$ = \$pi r^2\$
4	Step	Cancel out common factor.	\$81 \cancel{\pi}\$ = \$\cancel{\pi} r^2\$ 81 = \$r^2\$
5	Step	Solve for r.	81 = \$r^2\$ \$\sqrt{81}\$ = r 9 = r r = 9
6		Answer	The radius is 9cm.

Step

Type

Explanation

Answer

Problem

The area of a circle is \$81 picm^2\$. Find the radius.

Formula:

Area of a circle.

A = \$pi r^2\$

Step

Substitute \$81 \pi\$ for A

\$81 \pi\$ = \$pi r^2\$

Step

Cancel out common factor.

\$81 \cancel{\pi}\$ = \$\cancel{\pi} r^2\$
81 = \$r^2\$

Step

Solve for r.

81 = \$r^2\$
\$\sqrt{81}\$ = r
9 = r
r = 9

Answer

The radius is 9cm.