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Question
Find the cube of : 3a- 2b
Sum
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Solution
( a - b )3 = a3 - 3ab( a - b ) - b3
( 3a - 2b )3 = (3a)3 - 3 x 3a x 2b( 3a - 2b) - (2b)3
= 27a3 - 18ab( 3a - 2b ) - 8b3
= 27a3 - 54a2b + 36ab2 - 8b3
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