[محمد ابورهف]

س(س+3) (س+2)(س+1) + 1 = (س2 + 3س ) ( س2 +3س +2 ) + 1
= (س2 + 3س )( س2 +3س +1+1) + 1 = (س2 +3س +1-1 ) ( س2 +3س +1 +1 ) +1

= (س2 + 3س +1 )2 -1 +1 = (س2 + 3س +1 )2