Past exam of the mathematics course of the University of Cambridge / 2003 / ib / Paper 2 / 15E / d / Solution

Choose a fixed reference basis and let $V,W$ have columns $v_i,w_i$. Both matrices are invertible. The vectors $v_i+\lambda w_i$ are dependent exactly when $\det (V+\lambda W)=0$. This is a polynomial in $\lambda$ of degree $m$, whose leading coefficient is $\det W\ne 0$. A nonzero degree-$m$ polynomial has at most $m$ distinct real roots. Thus there are at most $m$ exceptional parameters. This is the determinant argument for the matrix pencil $V+\lambda W$.