We can use the pathagorian theorum: A²+B²=C² now in this case it would be X²+Y²=2² we also know that X and Y are the same number in this problem because they have the same corresponding angle (triangle angles always add to 180 and since we know 2 of the angles are 45 and 90 the remaining angle will also be 45) Because of this we can change our equation to Z²+Z²=2² (I'm using Z so that we do not confuse it with another letter we've already used) from there we can go to Z∧4=2² and then we will solve the equation. Z=√2 Z also equals X and Y therefore Y=√2
I hope this helps and please let me know if there is anything you don't understand I would be happy to clarify!
