f(x)=a*x*x+b*x+c
g(x)=0.521*x*(x-1)+x
fit f(x) "1a.txt" via a,b,c
unset key
set grid
set size square 0.6, 0.7
set term png
set output "graph1.png"
set xrange [-0.1:1.1]
set yrange [-0.1:1.1]
plot f(x) with lines, g(x) with lines, "1a.txt"