There is a right isosceles triangle. the hypotenuse is 31. find the value of the two missing legs. round the answer to the nearest 100th. if possible, i would like to learn the formula for future reference.

We know that
A right isosceles triangle  has two equal sides and two equal angles
so 
has two angles equals to 45°

methodology 1 to solve the problem
Let 
x> length of the leg of triangle
sin 45°=opposite side/hypotenuse
sin 45°=√2/2
opposite side=hypotenuse*sin 45°> 31*√2/2---> 21.92 units

methodology 2 to solve the problem
c²=a²+b²
c=hypotenuse> 31 units
a=leg 1
b=leg 2
a=b
so
c²=2a²> a²=c²/2> a²=(31)²/2
a=√[(31)²/2]> a=31/√2> 31√2/2> 21.92 units