动圆圆心M(x,y),动圆半径r,A(2,0)
则|MA|=r,(1)
动圆与圆C:(x+2)^2+y^2=2内切
|MC|=r-√2 (2)
(1)(2)得：
|MC|=|MA|-√2
即|MA|-|MC|=√2
∴M点轨迹是以C,A为焦点的
双曲线的左支
c=2,a=√2/2,b^2=c^2-a^2=4-2/4=7/2
动圆圆心M的轨迹:2x^2-2y^2/7=1 (x≤-√2/2)
双曲线的左支