# Question on Newton's Laws [duplicate]

Newton's first law can be derived from his second law. Then why did he put forth the first law, when it's already contained in second law?

My teacher was saying that first law is valid for an inertial reference frame, while second law is also valid for non-inertial reference frame. Is that correct? (I don't think so, as I knew Newton's laws are invalid in non-inertial reference frame.)

$$F=0 \implies a=0$$