Try:
%create a cater plot
clear all;
%x = [20,30,40,50]
x = [-3,-1,1,2]
y = [8,23,28,34]
y=[8,23,28,34].'
colum = [1,1,1,1]
matrixA1 =[]
matrixA2 = []
matrixA3 = []
equation = (x -35)/ 5
%create a matrix
% first matrix
matrixA1 = [colum(:),x(:)]
% secon matrix
new_vector = x.^2
matrixA2 = [colum(:), x(:), new_vector(:)]
% third matrix
new_vector3 = x.^3
matrixA3 = [colum(:), x(:), new_vector(:), new_vector3(:)]
%create the tranpose matrix
tranposeA = matrixA1.';
tranposeB = matrixA2.';
tranposeC = matrixA3.';
% power 1
final_matrixA = [tranposeA*matrixA1 tranposeA*y];
%power 2
final_matrixB = [tranposeB*matrixA2 tranposeB*y];
%power e
final_matrixC = [tranposeC*matrixA3 tranposeC*y];
A1 = rref(final_matrixA);
A2 = rref(final_matrixB);
A3 = rref(final_matrixC);
% for matrix A
a = A1(1,3);
b = A1(2,3);
%q = a+bx
i = -10:10
q = a +b*i
% for matrix b
a1 = A2(1,4);
b1 = A2(2,4);
c1 = A2(3,4);
q1 = a1 +b1*i+c1*i.^2
% matrix c
a2 = A3(1,5);
b2 = A3(2,5);
c2 = A3(3,5);
d2 = A3(4,5)
q2 = a2 +b2*i+c2*i.^2+d2*i.^3
% Plot
figure
hold on
plot(x,y,"O",'MarkerSize', 4);
plot(i,q,i,q1,i,q2)
hold off
