1 . a2+b2+c2 =
Answer: Option D
Explanation:
a + b + c = 9,
ab + bc + ca = 31,
a² + b² + c² = ?
(a + b + c)² = a² + b² + c² + 2(ab + bc + ca)
বা, a² + b² + c² = (a + b + c)² - 2(ab + bc + ca)
= 9² - (2×31)
= 81 - 62
= 19.
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