If (a + b + c) = 16, and (a2 + b2 + c2) = 90, find the value of (ab + bc + ca).
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. 83.
a + b + c = 16
a2 + b2 + c2 = 90
(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca)
⇒ (16)2 = 90 + 2(ab + bc + ca)
⇒ 256 = 90 + 2(ab + bc + ca)
⇒ 2(ab + bc + ca) = 166
⇒ ab + bc + ca = 83