What is the value of $a^2+b^2+c^2$, if a + b + c = 9 and ab + bc + ca = 23 ?
Answer & explanation
Correct answer: option 4
If a + b + c = 9
ab + bc + ca = 23
If the number of equation is less then the number of variables then we can put the extra variables according to our choice.
Here the number of variables are 3 and the number of equations are two than put c = 0
a + b = 9
ab = 23
$a^2+b^2+0$ = ?
( a + b )2 = a2 + b2 + 2ab
( 9 )2 = a2 + b2 + 2 × 23
a2 + b2 = 81 - 46 = 35