Question

求过L1:2x+y-5=0和L2:4x+y-9=0的交点,且平行于L3:x+2y-5=0的直线方程

Answer 1

∵2x+y-5=4x+y-9 => x=7,y=-9 这里解方程错了,得到的是x=2 y=1

∴直线L1与直线L2的交点为A(7,-9)

∵x+2y-5=0

∴y= -1/2x+5/2 => k=-1/2

∵设该直线为L4:y=-1/2x+b

∴代入点A得 -9= -7/2+b => b= -11/2

即L4:x+2y+11=0

由于交点错了,后面也就随之错了