restart

with(plots):

delta := 0.5

alpha := proc(n);
1/(1 + n)
end proc;

D1 := proc(n);
product(3*delta*alpha(k) - alpha(k) + 1, k = 1 .. n) - product(1 - alpha(k)*(1 - delta), k = 1 .. n)
end proc;

points:= {seq([alpha(n), D1(n)], n = 1 .. 100)};

pointplot(points);