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一、平面直角坐标系中点坐标的确定例1(2010年中国台湾)在坐标平面上,第二象限内有一点P,且P点到x轴的距离是4,到y轴的距离是5,则P点坐标为().A.(-5,4) B.(-4,5)C.(4,5) D.(5,-4)解析:做题时先画图,如图1,过点P分别向x轴、y轴作垂线,因为P点在第二象限内,并且到x轴的距离是4,到y轴的距离是5,所以垂足在x轴、y轴上对应的数分别为-5,4,故点P的坐标为(-5,4).答案为A.点评:过点P分别向x轴、y轴作垂线时,最好把P点到x轴和P点到y轴的距离表示出来,这样再找垂足在x轴、y轴上对应的数时才不会出现错误.注意点P(a,b)到x轴的距离为|b|,到y轴的距离为|a|.
Example 1 (China Taiwan in 2010) On the coordinate plane, there is a point P in the second quadrant, and the distance from point P to the x axis is 4 and the distance to the y axis is 5 , Then the coordinate of point P is () .A. (- 5,4) B. (- 4,5) C. (4,5) D. (5, -4) 1, too point P, respectively, to the x-axis, y-axis vertical, because the P-point in the second quadrant, and the distance to the x-axis is 4, the distance to the y-axis is 5, so the foot in the x-axis, y The corresponding number on the axis are -5,4, the coordinates of the point P is (-5,4). The answer is A. Comments: When the point P is perpendicular to the x-axis and the y-axis respectively, it is better to put P Point to the x-axis and the distance from the point P to the y-axis is shown, so that when finding the corresponding number of the foot-drop in the x-axis and y-axis, no error occurs. Note the distance from the point P (a, b) to the x-axis Is | b |, the distance to the y-axis is | a |.