（x-2)*(x-2)+y*y=3
x-2=√3sint
x=√3sint+2
y=√3cost
x-y=√3sint+2+√3cost
=2+√3(sint+cost)
=2+√3(sint+cos(兀/2-(兀/2-t))
=2+√3(sint+sin(兀/2-t)
=2+√3*2sin兀/2/2cos(t-(兀/2-t))/2
=2+2√3sin兀/4cos(t-兀/4)
=2+2√3*√2/2cos(t-兀/4)
=2+√6cos(t-兀/4)
所以最大值是 2+√6 最小值是2-√6