Give two numbers $a$ and $b$ which are algebraic over $\mathbb{Q}$ with $[\mathbb{Q}(a):\mathbb{Q}]=2$, $[\mathbb{Q}(b):\mathbb{Q}]=3$, but the degree of the minimal polynomial for $ab$ is smaller than $6$.
I have no idea how to approach. If you can't give me an answer, I'd appreciate a starting point suggestion. Thanks so much.