Question

If a+b+c=5 &ab+bc+ca=10 then proof that a square + b square +c square-3abc=-25

Answer 1

(a + b + c)² = a² + b² + c² +2(ab+bc+ca)

5² = a² + b² + c² +20

a² + b² + ² = 25 - 20 =5

a³ + b³ + c³ - 3abc = (a+b+c) (a² + b² +c² - (ab + bc + ac)

a³ + b³ + c³ - 3abc = 5   x  (5 - 10)

a³ + b³ + c³ - 3abc = ⁻25

Sorry question is wrong it should a³ + b³ + c³ - 3abc = ⁻25