Given:
The area of a sector =
![9\pi\text{cm}^2](https://img.qammunity.org/2022/formulas/mathematics/high-school/o8e77868c5g8thjkj2y6qcpt9lkgcuizfn.png)
The sector cover
of the entire circle.
To find:
The radius of the circle.
Solution:
Let r be the radius of the circle. Then, the area of the circle is:
![A=\pi r^2](https://img.qammunity.org/2022/formulas/business/college/s1qqgnrpw62vud6pcbwbec5snrl2vnma0w.png)
It is given that the sector cover
of the entire circle. So, the area of the sector is equal to
of the area of the entire circle.
![9\pi=(1)/(4)* \pi r^2](https://img.qammunity.org/2022/formulas/mathematics/high-school/v6lgcwv5n7dm2a2cieb2dbqn39yzc5erc6.png)
Multiply both sides by 4.
![36\pi =\pi r^2](https://img.qammunity.org/2022/formulas/mathematics/high-school/r8ogd1bna959a4n0k1um0m8yiqw0kev1bd.png)
Divide both sides by
.
![36 =r^2](https://img.qammunity.org/2022/formulas/mathematics/high-school/5nby73lsn82gdfobip7yhhrco3eozpcam5.png)
Taking square root on both sides.
![\pm √(36) =r](https://img.qammunity.org/2022/formulas/mathematics/high-school/vpecwlj4rzm54la1jguozlslnhyua9xext.png)
![\pm 6 =r](https://img.qammunity.org/2022/formulas/mathematics/high-school/kon79dahob87whegmrvfh1h8ya364qytov.png)
Radius of a circle cannot be negative. So,
.
Therefore, the radius of the circle is 6 cm.