Question

what is the formula of
(x+y+z)^2​

Answer 1

hope it helps you out dude

Answer 2

(x + y + z)2 = x2 + y2 + z2 + 2xy + 2yz + 2zx


Proof: 

Let x + y = k then, 

(x + y + z)2 = (k + z)2 

      = k2 + 2kz + z2        (Using identity I) 

      = (x + y)2 + 2(x + y)z + z2 

      = x2 + 2xy + y2 + 2 xz + 2yz + z2 

      = x2 + y2 + z2 + 2xy + 2yz + 2zx (proved)