Question

answer is (3).27

NEED EXPLANATION​

Answer 1

EXPLANATION.

=> a + b + c = 9

=> a² + b² + c² = 27

To find = ab + bc + ca.

Formula of ( a + b + c)²

$\sf : \implies \: (a + b + c) {}^{2} = {a}^{2} + {b}^{2} + {c}^{2} + 2(ab + bc + ca)$

=> ( 9)² = 27 + 2 ( ab + bc + ca)

=> 81 = 27 + 2 ( ab + bc + ca )

=> 81 - 27 = 2 ( ab + bc + ca)

=> 54 = 2 ( ab + bc + ca)

=> 27 = ab + bc + ca

=> value of ( ab + bc + ca) = 27

Answer 2

Answer:

✡ Question ✡

➡ a + b + c = 9; a² + b² + c² = 27

⟹ ab+bc+ca

✡ Given ✡

▶ a + b + c = 9

▶ a² + b² + c² = 27

✡ To Find ✡

➡ ab+bc+ca = ?

✡ Formula Used ✡

➡(a+b+c)²=a²+b²+c² +2(ab+bc+ca)

✡ Solution ✡

▶ According to the formula ,

=> ( 9)² = 27 + 2 ( ab + bc + ca)

=> 81 = 27 + 2 ( ab + bc + ca )

=> 81 - 27 = 2 ( ab + bc + ca)

=> 54 = 2 ( ab + bc + ca)

=> 27 = ab + bc + ca

=> ab + bc + ca = 27

=> ab + bc + ca = $\bold{\large{\fbox{\color{blue} {27}}}}$

Hence, the value of ab+bc+ca = 27