1) If each row of M can represented as the linear combination of the other rows
then linear combination of all the rows (not other rows) will be zero.
Reason
Since each row of M can be represented as the linear combination of the other rows so we have
R1 = K2R2 + K3R3 + K4R4 + ............+KnRn
=> K2R2 + K3R3 + K4R4 + ............+KnRn - R1 = 0
=> K1R1 + K2R2 + K3R3 + K4R4 + ............+KnRn = 0 ( here k1 = -1 )
So, the linear combination of all the rows is zero.
2) Yes, linear combination means only add,substract,multiply and divide not any other operation.