The square's diagonal is the triangle's hypotenuse.
the original Pythagorean theorem is

where
a and
b are the two sides and
c is the hypotenuse.
that means the Pythagorean theorem for this question is:

or
1. 40
2. 43
its just like subtracting when you add a negative number to a positive one. flip them around! makes it a lot easier.
Answer:
The length of diagonal XU is 6.40 units
Step-by-step explanation:
* Lets explain how to find the distance between two points
- The rule of the distance between two points 
and
is:

* Lets solve the problem
-From the attached figure:
- The coordinates of the vertex X are (2 , 2)
- The coordinates of the vertex U are (-2 , 7)
∴ The point
= (2 , 2)
∴ The point
= (-2 , 7)
∴ 
∴ 
∵ 
∴ 
∵ 
∴ d = 6.40
* The length of diagonal XU is 6.40 units
I think it's the one u picked