Given the following matrix A, find an invertible matrix U so that A is equal to UR, when R is the reduced row-echelon form of A: express in fraction form A: Solution A= 1 -2 3 7 23 1 0 9 19 31 -1 1 -5 -11 -24 NR2=R2-R1 ,NR3=R3+R1 1 -2 3 7 23 0 2 6 12 8 0 -1 -2 -4 -1 NR1=R1+R2.