In the rectangular coordinate system above, if P, not shown, is a point on AB and if the x-coordinate of P is 1, what is the y-c

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问题
In the rectangular coordinate system above, if P, not shown, is a point on AB and if the x-coordinate of P is 1, what is the y-coordinate of P?

选项 A、4/3
B、3/2
C、7/3
D、5/2
E、8/3

答案A

解析 上图所示的直角坐标系中,若P(未标出)是AB上一点,且P的横坐标为1,那么P的纵坐标为多少?
解:本题的正确答案为(A)。先写出直线AB的方程,然后把P点的坐标代入即可:y/2 + x/3 =1或y=-2/3 x +2。由此方程可得当x=1时,y=4/3。若考生对直线方程不太熟悉,则可以借助相似三角形的性质来解此题。显然由虚线切出的小三角形与△ABO相似,由此可推出y/2=(3-1)/3→ y=4/3
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