reset
set border
set xtics 1
set grid
set xzeroaxis lt 2 lw 2
set yzeroaxis lt 2 lw 2
set style line 1 lw 3
set xrange [-10:10]
set yrange [-20:10]
f(x)=x**2-2*x-15
g(x)=x+2
h(x)=f(x)/g(x)
plot h(x) ls 1,x-4 lw 3