Q1 of 36 Page 27

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(7x – 9y)3

(7x – 9y)3 =(7x)3 – [ 3 ×(7x)2 × 9y ] + [ 3 ×(7x)×(9y)2 ] –(9y)3


{ ∵(a – b)3 = a3 – 3a2b + 3ab2 – b3 }


= 343x3 – [ 3 × 49x2× 9y ] + [ 3 × 7x × 81y2 ] – 729y3


= 343x3 – 1323x2y + 1701xy2 – 729y3


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