For P:{ 1, 2} Q:{ 1, 2,3},

Obviously, the p range is smaller than the q range,

So p is a necessary and sufficient condition for q.

For p: Sina ≠ 1/2 Q:a≠5π/6.

Suppose the range of a is [0,2 π]

The range of p is a≠π/6 or a≠5π/6.

Obviously, the p range is smaller than the q range.

So p is a necessary and sufficient condition for q.

We should not take the judgment of necessary and sufficient conditions in simple logic for granted, but should think carefully.

Again, it is a sufficient condition, not a necessary condition, to push small scale to large scale.

This sentence is applicable to the judgment of a< necessary and sufficient conditions, whether it is set ({x, y, z}) or inequality (a