If a² + b² + c² = 14 and a + b + c = 6, then

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If a² + b² + c² = 14 and a + b + c = 6, then the value of (ab + bc + ca) is,

1. 11
2. 12
3. 13
4. 14

Correct Option: A

a² + b² + c² = 14 ..... (i)
a + b + c = 6
∴ (a + b + c)² = 6² = 36
⇒ a² + b² + c² + 2 (ab + bc + ca) = 36
⇒ 14 + 2 (ab + bc + ca) = 36
⇒ 2 (ab + bc + ca) = 36 – 14 = 22

⇒ ab + bc + ca =	22	= 11
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