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Step-3

Title: Area of semicircle

Grade: 7-a Lesson: S1-L4

Explanation:

Step	Type	Explanation	Answer
1	Problem	The radius of a circle is 42m.Find the area?
2	Formula:	Area of a semicircle.	A = \$\frac{\pi r^2}{2}\$
3	Step	Substitute \$22/7\$ for \$pi\$ and 42 for r.	A = \$\frac{\frac{22}{7} (42)^2}{2}\$ A = \$\frac{\frac{22}{7} \times 42 \times 42}{2}\$
4	Step	Cancel out common factor.	A = \$\frac{\frac{22}{\cancel{7}^1} \times \cancel{42}^6 \times 42}{2}\$
5	Step	Multiply.	A = \$\frac{\frac{22}{1} \times 6 \times 42}{2}\$ A = \$\frac{22 \times 6 \times 42}{2}\$
6	Step	Divide.	A = \$\frac{5544}{2}\$ A = \$\frac{\cancel{5544}^{2772}}{\cancel{2}^{1}}\$
7	Step	Answer.	A = 2772
8		Answer	The area is \$2772 cm^2\$

Step

Type

Explanation

Answer

Problem

The radius of a circle is 42m.Find the area?

Formula:

Area of a semicircle.

A = \$\frac{\pi r^2}{2}\$

Step

Substitute \$22/7\$ for \$pi\$ and 42 for r.

A = \$\frac{\frac{22}{7} (42)^2}{2}\$
A = \$\frac{\frac{22}{7} \times 42 \times 42}{2}\$

Step

Cancel out common factor.

A = \$\frac{\frac{22}{\cancel{7}^1} \times \cancel{42}^6 \times 42}{2}\$

Step

Multiply.

A = \$\frac{\frac{22}{1} \times 6 \times 42}{2}\$
A = \$\frac{22 \times 6 \times 42}{2}\$

Step

Divide.

A = \$\frac{5544}{2}\$
A = \$\frac{\cancel{5544}^{2772}}{\cancel{2}^{1}}\$

Step

Answer.

A = 2772

Answer

The area is \$2772 cm^2\$