Why tcp connect termination need 4-way-handshake?

Question

When connection sets up, there is:

Client ------SYN-----> Server

Client <---ACK/SYN---- Server ----①

Client ------ACK-----> Ser

Answer 1

From Wikipedia - "It is also possible to terminate the connection by a 3-way handshake, when host A sends a FIN and host B replies with a FIN & ACK (merely combines 2 steps into one) and host A replies with an ACK.[14]"

Source:

Wikipedia - https://en.wikipedia.org/wiki/Transmission_Control_Protocol

[14] - Tanenbaum, Andrew S. (2003-03-17). Computer Networks (Fourth ed.). Prentice Hall. ISBN 0-13-066102-3.