x=[0 1 3 4] 

y=[5 6 6 7] 

A=[x;ones(1,4)]' 

B=A'*A 

c=A'*y' 

B\c 

polyfit(x,y,1) 

polyfit(x,y,2) 

p1=polyfit(x,y,1) 

x0=linspace(-1,5,100); 

y0=polyval(p1,x0) 

plot(x,y,'*',x0,y0) 

A=[cos(x);sqrt(x);ones(1,4)]' 

B=A'*A 

c=A'*y' 

B\c 

y1=0.8209*cos(x0)+1.6390*sqrt(x0)+4.0822; 

plot(x,y,'x',x0,y1) 

A=[cos(x);sqrt(x)]' 

B=A'*A 

c=A'*y' 

B\c 

y2=3.7081*cos(x0)+4.9493*sqrt(x0); 

plot(x,y,'x',x0,y1,x0,y2) 

x,y 

p3=polyfit(x,y,3) 

y3=polyval(p3,x0) 

plot(x,y,'x',x0,p3) 

plot(x,y,'x',x0,y3)