Factorise: x2+y2+2(xy+yz+zx)
= x2+y2+2xy+2yz+2zx [we can take the first 3 terms as (x+y)2 and can take common 2z from last two terms]
= (x+y)2+2z(y+x) [we can take (x+y) common from both the terms and thus we got our answer]
= (x+y)(x+y+2z).