题目内容
(请给出正确答案)
[单选题]
点 M(4,-2) 、N(4,3) 在直线上,则直线的斜率k=()
A.0
B.-5
C.5
D.不存在
答案
由题意可得直线l得方程为y= 4 3 (x-2) 联立方程 y= 4 3 (x-2) y 2 =2x 8x 2 -41x+32=0 设A(x 1 ,y 1 )B(x 2 ,y 2 )M(x 0 ,y 0 ),则 x 1 + x 2 = 41 8 , x 1 x 2 =4 , y 1 + y 2 = 4 3 ( x 1 + x 2 -4) = 3 2 (1) x 0 = x 1 + x 2 2 = 41 16 , y 0 = y 1 + y 2 2 = 3 4 P,M两点间的距离PM= ( 2- 41 16 ) 2 +( 0- 3 4 ) 2 = 15 16 (2)由(1)可得M点的坐标 ( 41 16 , 3 4 ) (3) AB= ( x 1 - x 2 ) 2 +( y 1 - y 2 ) 2 = ( 1+ 16 9 )[ (x 1 + x 2 ) 2 -4 x 1 x 2 ] = 25 9 ( 41 2 64 -16 ) = 5 8 73
![](https://lstatic.shangxueba.com/sxbcn/h5/images/tips_org.png)