reset set border set xtics 1 set ytics 2 set grid set xzeroaxis lt 9 lw 3 set yzeroaxis lt 9 lw 3 set style line 1 lt -1 lw 4 set style line 2 lt 5 lw 3 set style line 3 lt 12 lw 3 set xrange [-10:10] # set yrange [-5:18] set samples 1000 set key off a=5 b=9 f(x)=sqrt((-b**2)*(1-(x**2)/a**2)) g(x)=-sqrt((-b**2)*(1-(x**2)/a**2)) plot f(x) ls 1, g(x) ls 1