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If 3x – 4y = 5 and Xy = 3, Find : 27x3 – 64y3. - Mathematics

Sum

If 3x – 4y = 5 and xy = 3, find : 27x3 – 64y3.

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Solution

27x3 – 64x3 = (3x)3 – (4y)3

= (3x − 4y)3 (3x − 4y)3 + 3 (3x) (4y) (3x − 4y) ......[ ∵ a3 − b3 = (a − b)3 + 3ab(a − b)]

= (5)3 + 36(xy) (3x − 4y)

= 125 + 36 (3) (5)

= 125 + 540 

= 665

Concept: Application of Formulae
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APPEARS IN

Selina Concise Mathematics Class 8 ICSE
Chapter 12 Identities
Exercise 12 (D) | Q 12 | Page 155
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