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Simplify: (3x – 4y)^3 + (4y – 5z)^3 + (5z – 3x)^3 - Mathematics

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Question

Simplify:

(3x – 4y)3 + (4y – 5z)3 + (5z – 3x)3

Simplify
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Solution

Given: (3x – 4y)3 + (4y – 5z)3 + (5z – 3x)3

Step-wise calculation:

1. Let a = 3x – 4y, b = 4y – 5z, c = 5z – 3x.

Note that a + b + c = (3x – 4y) + (4y – 5z) + (5z – 3x) = 0.

2. There’s a well-known algebraic identity: If a + b + c = 0, then a3 + b3 + c3 = 3abc.

3. Therefore, (3x – 4y)3 + (4y – 5z)3 + (5z – 3x)3 = 3(3x – 4y)(4y – 5z)(5z – 3x).

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Chapter 3: Expansions - Exercise 3A [Page 65]

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Nootan Mathematics [English] Class 9 ICSE
Chapter 3 Expansions
Exercise 3A | Q 19. (i) | Page 65
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