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Factorise : 25(2a - B)2 - 81b2 - Mathematics

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Question

Factorise : 25(2a - b)2 - 81b2

Sum

Solution

25(2a - b)2 - 81b2
= [ 5( 2a - b )]2 - (9b)2
= [ 5( 2a - b ) - 9b ][ 5( 2a - b ) + 9b ]               
                                          [ ∵ a2 - b2 = ( a + b )( a - b )]
= [ 10a - 5b - 9b ][ 10a - 5b + 9b ]
= [ 10a - 14b ][ 10a + 4b ]
= 2 x ( 5a - 7b ) x 2 x ( 5a + 2b )
= 4( 5a - 7b )( 5a + 2b )

shaalaa.com
Method of Factorisation : Difference of Two Squares
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Chapter 5: Factorisation - Exercise 5 (C) [Page 72]

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Selina Concise Mathematics [English] Class 9 ICSE
Chapter 5 Factorisation
Exercise 5 (C) | Q 4 | Page 72
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