Let A be a 7 times 4 matrix What must a and b be in order to
     Let A be a 7 times 4 matrix. What must a and b be in order to define T RarightarrowRb by T(x) = Ax ? a =   
  
  Solution
a=4
If one considers the matrix as a linear transformation from Rn to Rm, then the column space of the matrix equals the image of this linear transformation.

