Linear Algebra Fundamentals

A $2\times2$ matrix has determinant $-2$. Geometrically, what does this tell you about the linear transformation?

If $\mathbf{u}=(1,2)$ and $\mathbf{v}=(3,-1)$, what is $\mathbf{u}+\mathbf{v}$?

Which matrix represents a $90^\circ$ counterclockwise rotation in $\mathbb{R}^2$?