Explanation:
Keep in mind that this triangle is a 45-45-90 triangle meaning that it's isosceles
This means that the other side is also equal to s
The best way to solve this is by using the pythagorean theorem
+
=

10
= c (because it's the hypotenuse or the longest side)
s = a
s= b
Substitute the values into the formula stated above
+
=

+
=(10


Simplify
=

= 102
Now continue simplifying till you completely solve it
=

= 51
=

s=

I hope this helps!!!