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प्रश्न
If a2 + b2 + c2 = 41 and a + b + c = 9; find ab + bc + ca.
योग
उत्तर
(a + b + c)2 = (9)2
a2 + b2 + c2 + 2ab + 2bc + 2ca = 81
⇒ 41 + 2(ab + bc + ca) = 81
⇒ 2(ab + bc + ca)
= 81 - 41
= 40
⇒ ab + bc + ca
= 20.
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