运用圆的参数方程
P(cosa-2,sina)0<=a<2π
（1）点P到直线的距离=|3cosa-6+4sina+12|/5
=|5sin(a+arccos(4/5))+6|/5
最小值为1/5,最大值为11/5
（2）x+y=cosa+sina-2
=√2sin(a+π/4)-2
最大值为√2-2,最小值为-√2-2
（3）(y-2)/(x-1)=(sina-2)/(cosa-3)
令t=tan(a/2)sina=2t/(1+t^2)cosa=(1-t^2)/(1+t^2)
(y-2)/(x-1)=(2t-2-2t^2)/(1-t^2-3-3t^2)
=(t^2-t+1)/(2t^2+1)
=1/2*(t^2+1/2-t+1/2)/(t^2+1/2)
=1/2*[1-(t-1/2)/(t^2+1/2)]
=1/2-1/2*(t-1/2)/[(t-1/2)^2+(t-1/2)+3/4]
=1/2-1/2*1/[(t-1/2)+3/4*1/(t-1/2)+1]
最小值为(3-√3)/4,最大值为(3+√3)/4
当且仅当t=(√3+1)/2和(1-√3)/2时,等号成立