If a + b + c = 7, a2 + b2 + c2 = 21 , then the value of (ab + bc + ca) is?
Answer & explanation
Correct answer: option 2
(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca)
(7)2 = 21 + 2(ab + bc + ca)
49 - 21 = 2(ab + bc + ca)
(ab + bc + ca) = 14
If a + b + c = 7, a2 + b2 + c2 = 21 , then the value of (ab + bc + ca) is?
Correct answer: option 2
(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca)
(7)2 = 21 + 2(ab + bc + ca)
49 - 21 = 2(ab + bc + ca)
(ab + bc + ca) = 14