Answer:
![D=9√(2)\ in](https://img.qammunity.org/2020/formulas/mathematics/high-school/qr7lgz72l4jp3dyxj33ioiuhbhy2gwzu69.png)
Explanation:
step 1
Find out the length side of the square
we know that
The perimeter pf the square is equal to
![P=4b](https://img.qammunity.org/2020/formulas/mathematics/high-school/g7wa6ldnhizfqgnpwa393kjltnuv5qqfec.png)
where
b is the length side of the square
we have
![P=36\ in](https://img.qammunity.org/2020/formulas/mathematics/high-school/oow8y5qxycg8qgo8e53wj3cebvv1zbsldt.png)
so
![36=4b](https://img.qammunity.org/2020/formulas/mathematics/high-school/6qh5s474d3sigf6w6h12d30mopa1d37jr4.png)
Solve for b
![b=36/4\\b=9\ in](https://img.qammunity.org/2020/formulas/mathematics/high-school/zbmczna6iit3f1hcj87iw5gdzor2pykkcz.png)
step 2
Find out the length of the diagonal applying the Pythagoras Theorem
Let
D -----> the length of the diagonal of the square
b ----> the length side of the square
we have that
![D^2=b^2+b^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/pk7w4qw8m85it056we1zqjv5b6jlqs3iep.png)
we have
![b=9\ in](https://img.qammunity.org/2020/formulas/mathematics/middle-school/y56r5a7soql7vhm3b683pkkolhpyp2plkd.png)
substitute
![D^2=9^2+9^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/su8vf0jaxlahtmj7qe23w0m34ntrg467a6.png)
![D^2=2(81)](https://img.qammunity.org/2020/formulas/mathematics/high-school/qrp0e1j4y1foeib8lo9de0w72cpnubwj75.png)
![D=√(162)\ in](https://img.qammunity.org/2020/formulas/mathematics/high-school/xwxywrtkqoma7ov00yigc83ffruycf87j7.png)
Simplify
![D=9√(2)\ in](https://img.qammunity.org/2020/formulas/mathematics/high-school/qr7lgz72l4jp3dyxj33ioiuhbhy2gwzu69.png)