1. what is the value of x? show all of your work.

Pythagorean Theorem: A^2 + B^2 = C^2 
We know A and C, let's find B by doing it backwards 

C^2 - A^2 = B^2 
4^2 - 7 (square root of 7 squared is just 7) = B^2 
16 - 7 = B^2 
9 = B^2 

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.