Is it true that there is a basis for R^4 that consists of five vectors?

Is it true that when an n*n matrix whose columns form a basis of R^n, then A is invertible?

If Span {u,v} = R^2 then {2u,u+v} is a basis for R^2.   Is this statement true?

Does the ordered set v, v, va form a basis for R^3? If not, which vectors would you subtract from the set and which standard basis vector can you add to the set to make it a basis for R^3? vi = (1,–1, –2) = (5, –4, –7) v = (-3, 1,0) Select all answers that are correct. O subtract vector v 1 from the set O no it does not form a basis for R^3 O subtract vector v_3 from the set O yes it forms a basis for R^3 O add vector e_1 O add vector e 2 subtract vector v_2 from the set O add vector e_3