u=10:4:50;
y=[10 20 25 30 40 50 55 60 65 70 75];
plot ( u,y)
grid,title('sistemul de indentificat');

sy=0;
su=0;
suy=0;
su2=0;
N=length(u);
for i=1:N
    sy=sy+y(i);
    su=su+u(i);
    suy=suy+u(i)*y(i);
    su2=su2+u(i)*u(i);
end

a=(su*suy-su2*sy)/(su*su-su2*N);
b=(suy*N-su*sy)/(su2*N-su*su);
c=(su*N-su2*sy)/(sy*sy-su*su);

ym=a*u.^2+b*u+c;
figure
plot(u,ym)
hold on
plot(u,y,':')