reset
set border
# set xtics 1
# set ytics 1
set grid
set xzeroaxis lt 9 lw 2
set yzeroaxis lt 9 lw 2
set style line 1 lt -1 lw 3
set style line 2 lt 5 lw 3
set style line 3 lt 12 lw 3
set xrange [-30:30]
set yrange [-0.1:4]
f(x)=3*x**2+1
g(x)=x**2+x+9
h(x)=f(x)/g(x)
plot h(x) ls 1