Circles: Area

1. $144\pi$ or $452.16$ inches. $$\eqalign{A&=\pi r^2\\A&=\pi\times 12^2\\A&=\pi \times 144\\A&=452.16}$$

2. $16\pi$ or $50.24$ inches. $$\eqalign{A&=\pi r^2\\A&=\pi\times 4^2\\A&=\pi \times 16\\A&=50.24}$$

3. $2.25\pi$ or $7.065$ feet. $$\eqalign{A&=\pi r^2\\A&=\pi\times 1.5^2\\A&=\pi \times 2.25\\A&=7.065}$$

4. $16\pi$ or $50.24$ mm. $$\eqalign{A&=\pi r^2\\A&=\pi\times 4^2\\A&=\pi \times 16\\A&=50.24}$$

5. $9$ feet. $$\eqalign{A&=\pi r^2\\81\pi&=\pi\times r^2\\81&=r^2\\9&=r}$$

6. $50625\pi$ or $158962.5$ feet. $$\eqalign{A&=\pi r^2\\A&=\pi\times 225^2\\A&=\pi \times 50625\\A&=158962.5}$$

7. $625\pi$ or $1962.5$ feet. $$\eqalign{A&=\pi r^2\\A&=\pi\times 25^2\\A&=\pi \times 625\\A&=1962.5}$$

8. $225\pi$ or $706.5$ feet. $$\eqalign{A&=\pi r^2\\A&=\pi\times 15^2\\A&=\pi \times 225\\A&=706.5}$$

9. $4$ feet. $$\eqalign{A&=\pi r^2\\50.24&=\pi\times r^2\\16&=r^2\\4&=r}$$

10. $36\pi$ or $113.04$ inches. $$\eqalign{A&=\pi r^2\\A&=\pi\times 6^2\\A&=\pi \times 36\\A&=113.04}$$