l:2x-y-4=0
y=0
x= 2
与x轴交点: (2,0)
2x-y-4=0
y = 2x-4
m1 = 2 = tan θ1
所得到的直线方程,斜度=m2
m2 = tan( π/4 + θ1)
= (1+tan θ1)/(1-tan θ1)
= -3
所得到的直线方程
y-0= m2(x-2)
y= -3(x-2)