Question

यदि a-b = 4 तथा ab = 21 तो a3-b3 का मान बताओ

Answer 1

$<b>Heya mate. (^_-). Solution below.$
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• (a - b) = 4


• Cubing both sides -

=> (a - b)³ = (4)³


• Using identity : (x - y)³ = x³ - y³ - 3xy(x - y),

=> a³ - b³ - 3ab(a - b) = 64

=> a³ - b³ - (3 × 21)(4) = 64

=> a³ - b³ - (3 × 21 × 4) = 64

=> a³ - b³ - 252 = 64

=> a³ - b³ = 64 + 252

=> a³ - b³ = 316

$<marquee>Hence, a³ - b³ = 316.</marquee>$
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Thank you.. ;-)