若点M到两条互相垂直的直线的距离相等,求点M的轨迹方程. 答案:解析:取已知两条互相垂直的直线为坐标轴,建立直角坐标系,如上图所示.设点M的坐标为(x,y),点M的轨迹就是到坐标轴的距离相等的点的集合P={M||MR|=|MQ|},其中Q、R分别是点M到x轴、y轴的垂线的垂足.因为点M到x轴、y轴的距离分别是它的纵坐标和横坐标的绝对值,所以条件|MR|=|MQ|可写成|x|=|y|,即x±yOne third of the country_____ covered with
trees and the majority of the citizens______ black people.
A.is; are
B.is; is
C.are; are
D.are; is