If a + b + c = 0 and $a^2 + b^2 + c^2 = 40 $, then what is the value of 4ab + 4bc + 4ca ?
Answer & explanation
Correct answer: option 4
If a + b + c = 0
$a^2 + b^2 + c^2 = 40 $
what is the value of 4ab + 4bc + 4ca
( a + b + c )2 = ( a2 + b2 + c2 + 2(ab + bc + ca))
0 = 40 + 2(ab + bc + ca)
2(ab + bc + ca) = -40
4ab + 4bc + 4ca = 2 (2ab + 2bc + 2ca) = 2 × -40 = 80