Question

if a+b+c =8,a2+b2+c2=30 find ab+bc+ac​

Answer 1

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

⇒ 82 = 30 + 2(ab + bc + ca)

⇒ 2(ab + bc + ca) = 64 - 30

⇒ (ab + bc + ca) = 34/2 = 17

We know that, 

? a3 + b3 + c3 – 3abc = (a + b + c) (a2 + b2 + c2 – (ab + bc + ca))

⇒ 134 – 3abc = 8 × (30 – 17) = 104

⇒ 3abc = 134 - 104 = 30

⇒ abc = 30/3 = 10

∴ (abc)-1 = 1/10

Answer 2

$17 </p><p>$

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