Why is TCP three handshakes and four waves

Three handshakes , Mainly to prevent the failed connection request message from being sent to the server suddenly , So there's a mistake ;

The client sends ack=1,seq by x, The server sends... After receiving it ack=x+1,seq by y, The client receives and sends ack by y+

1 Officially establish its link

Four waves , Whoever initiates first , It's two-way

The client wants to terminate the link after it has no request to send , Is sent fin=1,seq by u, The server sends... After receiving it ack=u=1 Show that you have received ;

After the server has no data to send to the client , Is sent fin=1,que=v, The client receives and sends ack=v+1, The link officially ends