已知x平方+y平方+xy-3y+3,
=(x^2+xy+y^2/4)+(3y^2/4-3y+3)
=(x+y/2)^2+3(y/2-1)^2
=0
所以
x+y/2=0
y/2-1=0
y=2 x=-1
y^x=2^(-1)=1/2