令X=2012-a Y=2010-a X-Y=2 XY=2011
所以即为求 X²-Y²的值 X²-Y²=(X+Y)(X-Y)=√(X-y)²+4XY（X-Y)
=√2²+4X2011 X2=√4X2012 X2=4√2012=8√503