Suppose two propositions p, q
If the range of p is less than q, then p is a necessary and sufficient condition of q.
If the range of p is greater than q, then p is a necessary and sufficient condition for q.
If the two ranges are equal, this is a necessary and sufficient condition.
If the scope of the two does not coincide, then it is insufficient and unnecessary.
The point is that the method is not the answer. If you still don't understand my method, you can ask me.
If you understand, this question is not a problem for you, so I won't answer it here.
First of all, the above method, pay attention to, the topic requires what Q is P.
Let's see that the range of q is smaller than that of p. According to the above method, q is the necessary and sufficient condition of p.
On the other hand, we can see that the range of p is greater than q, and then sum up the above methods. P is a necessary and sufficient condition for q.
In this way, we can draw a conclusion that when P is the necessary and sufficient condition of Q, Q is also the necessary and sufficient condition of P, and they are the same.
Friendly reminder: be sure to read the topic carefully before writing.