a ( b2 + c2 + bc ) + b ( a2 + c2 + ac ) + c ( a2 + b2 + ab )
= ab2 + ac2 + abc + ba2 + bc2 + abc + ca2 + cb2 +abc
= ( ab2 + a2b + abc ) + ( ac2 + a2c + abc ) + ( bc2 + b2c + abc )
= ab ( a + b + c ) + ac ( a + b + c ) + bc ( a + b + c )
= ( a + b + c ) ( ab + ac + bc )
\(a\left(b^2+c^2+bc\right)+b\left(a^2+c^2+ac\right)+c\left(a^2+b^2+ab\right)\)
\(=ab^2+ac^2+abc+ba^2+bc^2+abc+ca^2+cb^2+abc\)
\(=\left(ab^2+ba^2+abc\right)+\left(bc^2+cb^2+abc\right)+\left(ca^2+ac^2+abc\right)\)
\(=ab\times\left(a+b+c\right)+bc\times\left(a+b+c\right)+ca\times\left(a+b+c\right)\)
\(=\left(a+b+c\right)\times\left(ab+bc+ca\right)\)