reset
set border
set xtics 1
set ytics 1
set grid
set xzeroaxis lt 9 lw 3
set yzeroaxis lt 9 lw 3
set style line 1 lt 1 lw 4 # red line
set style line 2 lt 3 lw 3 # blue line
set style line 3 lt 12 lw 3
set xrange [-14:14]
set yrange [-26:14]
# set samples 1000
# set key off
# An integer insection is formed for
# y = -(a/b)x+c 
# y = y = (d/e)x+c-ae-db
# The lines are perpendicular if e = ad/b
a=2
b=3
c=5
d=7
e=(a*d)/b
# e=11
# Dunno why, but f(x)=(d/e)*x+c-a*e-d*b fails to work
# I just discovered that the above is seriously flawed.
# 200607131522
# No time to fix it now, but the lines being drawn are -2x/3+5 and 1.75x-24!
f(x)=-(a*x/b)+c
g(x)=(d*x/e)+c-a*e-d*b
plot f(x) ls 1, g(x) ls 2