If a + b + c = 0 and $a^2 + b^2 + c^2 = 40 $, then what is the value of ab + bc + ca ?
Answer & explanation
Correct answer: option 2
If a + b + c = 0
$a^2 + b^2 + c^2 = 40 $,
Then what is the value of ab + bc + ca
If the number of equations are less than the number of variables then we can put the extra variables according to our choice =
So here two equations given and three variables are present so put c = 0
If a + b = 0
$a^2 + b^2 = 40 $,
Then what is the value of ab = ?
( a + b )2 = a2 + b2 + 2ab
( 0 )2 = 40 + 2ab
2ab = -40
ab = -20