a) (a + b+c)^2
= [(a+b)+c]^2
=(a+b)^2 + ..............................+ c^2
=a^2 +......................................+ c^2
=a^2 +.................................
b) (a + b - c)^2=.................................
=(a+b)^2 + ..............................+ c^2
=a^2 +......................................+ c^2
=a^2 +.................................
c)
(a - b - c)^2=.................................
=(a-b)^2 - ..............................+ c^2
=a^2 -......................................+ c^2
=a^2 +.................................
