If the system of linear equations x+y+z=a,   x−y+bz=2,2x+3y−z=1  has infinitely many solutions, then b−5a=

Augmented matrix =111a1-1b223-11                                    ~R2→R2−R1R3→R3 −2R1 111a0-2b-12-a01-31-2a                                   ~R3→2R3 +R2 111a0-2b-12-a01b-74-5aGiven system has infinitely many solutions⇒b−7=0,    4−5a=0b=7,            a=45b−5a=   7−5×45 =   7−4=3