（x+2）²+丨2y+1丨=0解:x+2=0 x=-22y+1=0 y=-1/2所以，x+y=（-2）+（-1/2）=-2又1/2
两个非负数之和=0，只有这两个数都=0时才有可能；∴x=2，y=-1/2；∴x+y=2-(1/2)=3/2；
(x-2)^2+丨2y+1丨=0=>x-2 =0 and 2y+1=0x=2 and y =-1/2x+y = 2 -1/2 = 3/2
