a0=1;
a1=2;
N=20;
x = rand(1,N)*100;
y0 = a0 + a1*sqrt(x);
y = y0 + randn(1,N) *0.5;

X = [ones(N,1), sqrt(x(:))];
a = (X'*X)^(-1)*X'*y(:),

xx = 0.1: 0.01:100;
yy = a(1)+a(2)*sqrt(xx);

figure(1)
clf;
plot(x,y,'bo'); grid on; hold on;
plot(xx,yy,'r');