For this, you will be using the pythagorean theorem, which is
. In this case, 3 and 7 are the hypotenuse and AB is the hypotenuse. Our equation is
![3^2+7^2=AB^2](https://img.qammunity.org/2019/formulas/mathematics/middle-school/hzo9kyekah9gxc542js0jugsx0kd66u419.png)
Firstly, solve the exponents:
![9+49=AB^2](https://img.qammunity.org/2019/formulas/mathematics/middle-school/6epyvoyeykq8xf7xhn5256a6et9airvngo.png)
Next, combine 9 and 49 to get
![58=AB^2](https://img.qammunity.org/2019/formulas/mathematics/middle-school/dmn2hb5cdyiz9jaetyjl5dd97gcjgvn7p2.png)
Lastly, square root both sides to get
![√(58)=AB](https://img.qammunity.org/2019/formulas/mathematics/middle-school/bwtb3w8orxyt5jheg8ikefr307hj1ct69k.png)
In short, the answer is √58 cm, or the last option.