设M（x,y)√[(x+4)²+y²]=2√[(x-2)²+y²]x²+8x+16+y²=4(x²-4x+4+y²)3x²+3y²-24x=0x²-8x+y²=0(x-4)²+y²=16∴动点M的轨迹方程是