QG Quant Review 2nd Edition - Question 73

If x^2 + y^2 = 29, what is the value of (x-y)^2? 1) xy = 10 2) x = 5 OA [spoiler]= A[/spoiler] So I understand that statement 1 is sufficient. But why isn't statement 2 sufficient? The answer explains that it is because statement 2 doesn't tell us what Y is. Why not? Why can't we substitute x=5 into...