I have a 6*6 matrix which is A:[1,1,1,1,1,1],[1,0,-1,1,0,-1],[2,1,0,2,1,0],[4,1,2,0,4,1],[1,-2,1,-6,0,1],[5,4,-1,-2,5,0]

How can I show the system Ax=b is consistent or inconsistent if

x= [x1          b= [1

     x2                 0 

     x3                 1

I have a matrix;   

                1   -4  1

A4:           0    7  5     

                 0    0   0

I created three different matrices which are A,B and C. I tried to calculate 4(AB)C but when I command it,it gives me an error. Does anyone know how can I do that?

I also need to create a system of three different linear equations with unknown that has one solution. My equations are 2x+3y=8 -x+2y=3 and 3x-4y=-5.Can anyone tell me how can I plot these lines, solve the system by using solve command and how can I solve the system using by matrices and row operations?