Using properties of determinants prove that:



[R1’ = 3R1]


[R1’ = R1 - R2]


[R2’ = 2R2]


[R2’ = R2 - R3]


= (1/6)[0 + 0 + 6a{a(a + b) - a(2a + b) [expansion by first column]


= - a3


1