Problem 3 Let A = (a - 4) -1 2 (a - 1) i) Use row operations to put A into upper triangular form using only type I and III operations [upper triangular means that A(i, j) = 0 whenever i > j. Make sure your operations are defined for all possible values of a (suggestion: avoid dividing by any expression which could be zero for certain values of a). ii) Use i) to find the values of a for which the matrix A is singular. iii) Assuming a to be a value different from those listed in ii), find an explicit expression for A- in terms of the indeterminate a, by computing rref ([A | I])