At the party, everyone shakes hands with others once, and everyone shakes hands 2 1 time. How many people are there at the party?

This problem can be solved by this equation. Suppose * * there are x people attending the party, and everyone only shakes hands with others once, then everyone needs to shake hands with x- 1 times, and x people need to shake hands with x(x- 1) times. A handshake is between two people, so * * and X (X-) shake hands.

Solution: Assuming that * * * there are x people attending the party, we can get the equation:

x(x- 1)÷2=2 1

x(x- 1)=42。

x=7

So there are seven people.