1. A linear system of three equations in five unknowns must have infinitely many solutions.

2. A matrix can have more than one echelon form.

3. If a1,a2, and a3 are vectors in R^3, the set Span{a1,a2,a3} necessarily contains some vectors that are not in the set Span{a1,a2,a3}

4. If the augmented matrix have apivot in every row, the system is inconsistent.

Please explain the reason, whatever they are true of false.

Thank you