How do i figure out the length of two unknown sides of an isosceles right triangle, when the hypotenuse is 8.6m (c=8.6m)?

Hey, for this problem, you are going to want to use SOH CAH TOA, {Sine, Cosine or Tangent} since the hypotenuse is involved, you can use sine or cosine. {I used Cosine}. 
cos(45°)=x/8.6                  {x is missing side}
0.7071=x/8.6
0.7071×8.6=x/8.6 ×8.6
6.08=x

P.S.: Hope I Helped :)
if you need further explaining just lmk