If a2 +b2 +c2 = 20 and ab + bc + ca = 10 , then the value of (a + b + c)2 is:
Show answer & explanation
Correct answer: C
Explanation
a² + b² + c² = 20
ab + bc + ca = 10
(a + b + c)² = a² + b² + c² + 2(ab + bc + ca)
(a + b + c)² = 20 + 2 × 10
= 20 + 20
= 40