Circle worksheet

1. Area: 84.05 square units

1. Find the radius (r) by working backward: the distance around (C) is 2 × π × r, so divide C by 2π

   $r$$=\frac{32.5}{2\times \pi }$$=5.172536$

2. Find the diameter (d), the distance straight across: it's twice the radius

   $d$$=2\times 5.172536$$=10.345071$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times {5.172536}^2$$=84.053704$

2. Area: 95.03 square units

1. Find the radius (center to edge): it's half the diameter, the distance straight across

   $r$$=\frac{11}{2}$$=5.5$

2. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 5.5$$=34.557519$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times {5.5}^2$$=95.033178$

3. Area: 50.27 square units

1. Find the radius (center to edge): it's half the diameter, the distance straight across

   $r$$=\frac{8}{2}$$=4$

2. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 4$$=25.132741$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times 4^2$$=50.265482$

4. Area: 50.27 square units

1. Find the diameter (d), the distance straight across: it's twice the radius

   $d$$=2\times 4$$=8$

2. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 4$$=25.132741$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times 4^2$$=50.265482$

5. Area: 38.48 square units

1. Find the radius (center to edge): it's half the diameter, the distance straight across

   $r$$=\frac{7}{2}$$=3.5$

2. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 3.5$$=21.991149$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times {3.5}^2$$=38.48451$

6. Radius: 4.72

1. Work backward from the area (A): it's π × the radius squared, so divide A by π to get the radius squared

   $r^2$$=\frac{70}{\pi }$$=22.281692$

2. Take the square root to undo the squaring, which gives the radius (r)

   $r$$=\sqrt{22.281692}$$=4.720349$

3. Find the diameter (d), the distance straight across: it's twice the radius

   $d$$=2\times 4.720349$$=9.440697$

4. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 4.720349$$=29.658826$

7. Radius: 4.89

1. Work backward from the area (A): it's π × the radius squared, so divide A by π to get the radius squared

   $r^2$$=\frac{75}{\pi }$$=23.873241$

2. Take the square root to undo the squaring, which gives the radius (r)

   $r$$=\sqrt{23.873241}$$=4.886025$

3. Find the diameter (d), the distance straight across: it's twice the radius

   $d$$=2\times 4.886025$$=9.77205$

4. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 4.886025$$=30.699801$

8. Area: 63.62 square units

1. Find the radius (center to edge): it's half the diameter, the distance straight across

   $r$$=\frac{9}{2}$$=4.5$

2. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 4.5$$=28.274334$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times {4.5}^2$$=63.617251$

9. Area: 113.1 square units

1. Find the diameter (d), the distance straight across: it's twice the radius

   $d$$=2\times 6$$=12$

2. Find the circumference (C), the distance around: 2 × π × the radius

   $C$$=2\times \pi \times 6$$=37.699112$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times 6^2$$=113.097336$

10. Area: 161.14 square units

1. Find the radius (r) by working backward: the distance around (C) is 2 × π × r, so divide C by 2π

   $r$$=\frac{45}{2\times \pi }$$=7.161972$

2. Find the diameter (d), the distance straight across: it's twice the radius

   $d$$=2\times 7.161972$$=14.323945$

3. Find the area (A), the space inside: π × the radius × the radius

   $A$$=\pi \times {7.161972}^2$$=161.14438$