1
x^2+y^2=2x+4y
(x-1)^2+(y-2)^2=5
参数方程：x=√5cost+1,y=√5sint+2
2x-y
=2(√5cost+1)-√5sint+2
=2√5cost-√5sint,假设tanp=2
=5sin(p-t)
p-t=-90,最小-5
p-t=90,最大5
2)
内切圆半径r
r=AC*BC/(AB+AC+BC)=1
以C为原点，两条直角边AC,BC为X，Y正半轴，建立平面直角坐标系，C(0,0),C(3,0),B(0,4),圆(x-1)^2+(y-1)^2=1
圆的参数方程：
x=cost+1,y=sint+1
PA^2+PB^2+PC^2
=(cost+1)^2+(sint+1)^2+(cost+1-3)^2+(sint+1-0)^2+(cost+1)^2+(sint+1-4)^2
=-2sint+20
18<=PA^2+PB^2+PC^2<=22
PA^2+PB^2+PC^2的最小值18
