Answer:
A
Explanation:
This is a 45 45 90 triangle since it has 45 and a 90 degree angle so using triangle interior theorem, the third angle is 45.
The legs of a 45 45 90 triangle are congruent so only A is right.
But since you want the work
The length of the hypotenuse in 45 45 90 triangle is sqr root of 2 times more than both of the legs so
let divide sqr root of 2 by the hypotenuse to find the legs.

To check our work let use the pythagorean theorem, since it a right angle







so it is correct.