# Basis and dimension on complex vector spaces

#### christianwos

Find the dimension of and a basis for the following subspaces of C^3:
(i) The set of all complex multiples of (1,i,1-i)

(ii) The plane z1+z2+(1-i)z3=0

(iii) The range of the matrix A with rows (1,i,2-i) and (2+i, 1+3i, -1-i)

(iv) The kernel of the same matrix.

(v) The set of vectors that are orthogonal to (1-i, 2i, 1+i).

Thank you

#### johnsomeone

*Presumably*, given your title and the implicit assumption when things are stated this way,

by the vector space $$\displaystyle \mathbb{C}^3$$, you mean the vector space over the base field $$\displaystyle \mathbb{C}.$$

For (i) maybe this is a case where abstraction clarifies rather than confuses? Maybe it removes the the jumble formed by the specific values?
Suppose I tell you I have a vector space V over a field F. Suppose I give you a fixed vector in V, and ask you to find a basis and the dimension of the subspace formed by all F-multiples of that vector:

$$\displaystyle \text{Let } V \text{ be a vector space over field } \mathbb{F}.$$

$$\displaystyle \text{Let } \vec{v_0} \in V - \{ \vec{0} \}. \text{ Let } W = \{ a\vec{v_0} \in V | a \in \mathbb{F} \}.$$

$$\displaystyle \text{What is the dimension of the subspace } W? \text{ What is a basis for } W?$$

You do everything *exactly* as you would for a real vector space, except now the coefficients are allowed to be complex numbers. That goes not just for problem (i), but for all 5 problems. Ask yourself, "How would I do the same problem, except for a real vctor space using real coefficients?" If you can answer that, then you should be able to solve these. Every procedure is *exactly* the same, except that here it uses complex coefficients.

Last edited:
1 person