If a2 + b2 + c2 = 390 and ab + bc + ca = 5, then a + b + c is
Choose the correct choice from the following answers:  A) 19  B) 20  C) 25  D) 30  E) 64

Rationale: by formula , ( a + b + c ) ^ 2 = a ^ 2 + b ^ 2 + c ^ 2 + 2 ( ab + bc + ca ) , since , a ^ 2 + b ^ 2 + c ^ 2 = 390 and ab + bc + ca = 5 , ( a + b + c ) ^ 2 = 390 + 2 ( 5 ) = 400 = 20 ^ 2 therefore : a + b + c = 20 answer : b
Answer: B