Expressions, Equations, and Relationships>Determining the Circumference and Area of Circles(TEKS.Math.7.9.B)

Use $C=2\pi r$ because the radius is given. $C=2(3.14)(7.5)=47.1\text{ cm}$ (about $47.10\text{ cm}$). Circumference uses linear units (cm), not square units.

Area uses $A=\pi r^2$. With diameter 24 ft, $r=12$ ft. $A=3.14(12)^2=3.14(144)=452.16\text{ square feet}$. Use square units for area.

For circumference with diameter, use $C=\pi d$. $C=3.14(9)=28.26\text{ inches}$. Circumference is a length (linear units), not square inches.

Use $A=\pi r^2$ because the radius is given. $A=3.14(3.2)^2=3.14(10.24)=32.15\text{ square meters}$. Area must be in square units.

Use $C=2\pi r$ for circumference with radius. $C=2(3.14)(14)=87.92\text{ inches}$. Circumference is linear, so do not use square units.