3.9

Let us consider a proof by contradiction: suppose: $\ell$, $m$, $n$ are distinct tangent lines, and suppose they meet in a point $P$. Consider the pole-polar relationship with respect to this conic. The poles of $\ell$, $m$, $n$ are three distinct points $L$, $M$, $N$ of the conic, whereas the polar of $P$ is a line $p$. However, $L$, $M$, $N$ must be incident with $p$; which is impossible because any line meets the conic in at most two points.