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If a2 + b2 + c2 = 1, then ab + bc+ ac lies in the interval
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1, 2 
3 -
- 1 1, 2 -
- 1, - 1 2 - [2, – 4]
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Correct Option: B
(a + b + c)2 >= 0
⇒ a2 + b2 + c2 + 2(ab + bc + ca) >= 0
⇒ 1 + 2(ab + bc + ca) >= 0
Thus, (ab + bc + ca) >= – 1/2
Similarly,using:
(a – b)2 + (b – c)2 + (c – a)2 >=1
We will get ab + bc + ca <= 1.
Hence, [–1/2, 1] will be the right answer.
