Hello everyone

I'm a new maple user, so I'm really sorry if this question is dumb, I've tried to find people with a similar problem but didn't find anyone.

So this is my problem: when I try to multiply a vector with a variable it gives me this:

> Restart; With(LinearAlgebra);
> B1 := [1, 2, 0, -1];
                         [1, 2, 0, -1]
> B2 := [0, 1, -1, 0];
                         [0, 1, -1, 0]
> A1 := a*B1+b*B2;