Answer :

naǫ
Use the Pythagorean theorem:
[tex](leg)^2+(leg)^2=(hypotenuse)^2 \\ 20^2+20^2=x^2 \\ 400+400=x^2 \\ x^2=800 \\ x=\sqrt{800} \\ x=28.28... \\ x \approx 28.3[/tex]

The length of the hypotenus is approximately 28.3 cm.