Question

If a square +b square +c square =83 and a+b+c = 15 ,then find the value of ab+bc+ca .

Answer 1

a + b + c = 15

(a + b + c )² = (15)²

a² + b² + c² + 2 ( ab + bc + ac ) = 225

83 + 2 ( ab + bc + ac ) = 225

ab + bc + ac = (225 - 83)/2

ab + bc + ac = 142/ 2

=71