InterviewSolution
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For|x|lt(1)/(5)thecoefficientofx ^ 3intheexpansion of(1)/((1 - 5x ) ( 1 - 4 x))is |
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Answer» 369 `= [ 1 + 5x+(5x ) ^ 2+ (5x ) ^3 + …. ][ 1+ 4x+ (4x) ^ 2+(4x ) ^3 + … ]` `therefore`Co- efficientof` x ^ 3` intheaboveexpansion `= (1)(4) ^3+ 5 (4)^2 + (5 ^ 2 ) (4)+1 (5) ^ 3 ` `= 64+80+ 100 +125 ` ` = 369 ` |
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