reset
set border
set xtics 1
set ytics 1
set xzeroaxis lt 9 lw 4
set yzeroaxis lt 9 lw 4
set style line 1 lt 1 lw 4
set style line 2 lt 3 lw 4
set style line 3 lt 10 lw 4
set style line 4 lt 12 lw 8
set style line 5 lt 9 lw 1
set grid ls 5
show grid
set xrange [-10:10]
set yrange [-15:15]
# set samples 1000
set key on
f(x)=0.5*x-1.5
g(x)=-x**2-9
h(x)=x**3-9*x
# i(x)=4*x**2+40*x+84
# plot f(x) ls 1
# plot f(x) ls 1,g(x) ls 2, h(x) ls 3, i(x) ls 4 
plot f(x) ls 1,g(x) ls 2, h(x) ls 4