reset
set border
set xtics 2
set ytics 2
set grid
set xzeroaxis lt 2 lw 2
set yzeroaxis lt 2 lw 2
set style line 1 lt 3 lw 3
set style line 2 lt 5 lw 3
set style line 3 lt 12 lw 3
set xrange [-10:10]
set yrange [-5:18]
k=16
r=8
f(x)=k+(-k*x*x)/(r*r)
plot f(x) ls 1