Assume new axiom 3+4= 8

(3+4) = 7
-(3+4) = -8
-------------
-0 = -1
0 = 1
Proof
Now, (X^n+Y^n) = (X^n+Y^n) - 0*(-0.5 + X^n+Y^n)
subsitute 0=1
= 0.5
A disproof
(X^n+Y^n) = (X^n+Y^n) - 0*(-2^n + X^n+Y^n)
subsitute 0=1
= 2^n

Why fermat's last theorem cannot be proved
A proof will wreck a mathematician's total revenue money. For example, a prize giving organization will be able to sustain itself for infinite number of years if fermat's last theorem was never proved and a prize was rewarded for such an activity.