Question

If a plus B plus C is equal to 11 and a2+b2+c2=71 then ab+bc+ca =?

Answer 1

Step-by-step explanation:

(a + b + c)2 = a2 +b2 + c2 + 2ab + 2bc + 2ca. ⇒ (a + b + c)2 = 83 + 2(ab + bc + ca). ⇒ (a + b + c)2 = 83 + 2 × 71. ⇒ (a + b + c)2 = 83 + 142.