mathematics formula important

 
1. (a+b)^2   = a^2+b^2+ 2ab.
2. (a-b)^2    = a^2+b^2- 2ab.
3. (a+b)^3   = a^3+b^3+3a^2+3ab^2.
4 (a-b)^3     = a^3- b^3-3a^2b+3ab^2.