A2 + b2 + c2 sama dengan?
Jawaban: (a + b + c)² = a² + b² + c² + 2 (ab + bc + ca)
Kita dapat menyelesaikan persamaan dengan mempertimbangkan (a + b + c) 2 menjadi (a + b + c)(a + b + c)
(a + b + c)(a + b + c) = a × (a + b + c) + b × (a + b + c) + c × (a + b + c)
(a + b + c)(a + b + c) = a 2 + ab + ac + ba + b 2 + bc + ca + cb + c 2
(a + b + c)(a + b + c) = a 2 + b 2 + c 2 + 2ab + 2bc + 2ca
(a + b + c)² = a 2 + b 2 + c 2 + 2 (ab + bc + ca)