Show that given vectors are not vector space basis in $R^4$

vector-spaces

The task is to show that the vectors $(1, 0, 0, 0)$, $(1, 1, 0, 0)$ and $(1, 1, 1, 0)$ are not vector space basis in $R^4$. I tried the method of getting a system of linear equations:
$\alpha(1, 0, 0, 0) + \beta(1, 1, 0, 0) + \gamma(1, 1, 1, 0) = (0, 0, 0, 0)$, which gives the result $\gamma = 0$ and consequently $\alpha = 0$ and $\beta = 0$ – and if I understand correctly, this would mean that the given vectors are the vector space basis in $\mathbb R^4$. How do I prove these vectors are not the vector space basis?

Best Answer

With your approach, what you can prove is that they are linearly independent — and they are. But in order be be a basis, they must span $\mathbb{R}^4$, and they don't. The space $\mathbb{R}^4$ has dimension $4$ and therefore no set with less than $4$ elements can span it.

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