If a + b + c = 7 and $a^3 + b^3 + c^3 -3abc = 301,$ then ab + bc + ca = ?

2

If a + b + c = 7

$a^3 + b^3 + c^3 -3abc = 301,$

then 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 = 7

$a^3 + b^3 = 301,$

then ab = ?

We know that,

(a + b)³ = a³ + b³ + 3ab(a+b)

(7)³ = 301+ 3ab(7)

343 = 301 + 21ab

21ab = 42

ab = 2