a2 + b2 + 2ab + 2bc + 2ca
As we know, p2 + q2 + 2pq = (p + q)2
We get,
= (a+b)2 + 2bc + 2ca
= (a+b)2 + 2c( b + a )
Or (a+b)2 + 2c( a + b )
Take (a + b) as common factor;
= (a + b)(a + b + 2c)
Therefore, a2 + b2 + 2ab + 2bc + 2ca
= (a + b)(a + b + 2c)