Question

已知两点P(-2,0),Q(2,0),M为坐标平面内的动点,满足｜｜·｜｜=·,则动点M(x,y)的轨迹方程为

A.y²=8x               B.y²=-8x               C.y²=4x                D.y²=-4x

Answer 1

B

解析:=(4,0), =(x+2,y),=(2-x,-y),

||·||=4,·=8-4x,

∵||·||=·,

∴=2-x.

∴x²+4x+4+y²=4-4x+x².

∴y²=-8x.