“Synergy = 2+2 = 5”, or "... effect which can produce a combined return on the firm’s resources greater than the sum of its parts.”
H. Igor Ansoff.

“Synergy = 2+2 = 5”, which means ​“Sharing of capabilities among units of the firm which produces performance which is greater than the performance which can be obtained if the units operate independently of one another.”  ​or "... effect which can produce a combined return on the firm’s resources greater than the sum of its parts.”
H. Igor Ansoff.