How to show that linear applications are closed and open

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Let $f: R^n\mapsto R^m$ a linear application.

Is $f$ closed? Why?

Is it open? Why?

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The projection $\pi_1: \mathbb{R}^2 \to \mathbb{R}$ is not closed.

Linear maps are open onto their image (open mapping theorem), between Euclidean spaces. Otherwise consider $f(x,y) = (x,0)$ on the plane.