There is this specific ratio for 45-45-90 triangles where the length of the hypotenuse is radical 2 times as long as a leg. With this in mind, we can create an equation where the length of one leg is represented with the variable x.
x

= 10
divide both sides by
x = 10

/
x = 10

/2
x = 5
The length of one leg is 5