(3). Let $$T: \mathbb{R}^n \to \mathbb{R}^m$$ be a linear transformation and $$A$$ be its standard matrix, that is, $$T \vec{x} = A \vec{x}$$ for each $$\vec{x} \in \mathbb{R}^n$$. Please show that the range of $$T$$ is just the column space of $$A$$. (10%)