How do you do this?

Answer:
Legs: [tex]x[/tex]
Hypotenuse: [tex]\sqrt{2}\cdot x[/tex]
Step-by-step explanation:
In this case, a 45-45-90 right triangle is a right triangle whose legs have the same length and hypotenuse is [tex]\sqrt{2}[/tex] times the length of any of the legs. Then, the dimensions of this triangle are, respectively:
Legs: [tex]x[/tex]
Hypotenuse: [tex]\sqrt{2}\cdot x[/tex]