Question

一动圆与圆A (x+5)^2+y^2=49和圆B (x-5)^2+y^2=1都外切,求动圆圆心P和其轨迹方程

Answer 1

P(x,y),A(-5,0),B(5,0),rA=7,rB=1PA=( (x+5)^2+y^2 )^0.5PB=( (x-5)^2+y^2 )^0.5PA-rA=PB-rB( (x+5)^2+y^2 )^0.5 - 7 =( (x-5)^2+y^2 )^0.5 - 1所以轨迹方程为：16x^2-9y^2=144