Maths-
General
Easy

Question

In the expansion of left parenthesis 1 plus x plus x to the power of 2 end exponent plus x to the power of 3 end exponent right parenthesis to the power of 6 end exponent comma then coefficient of x to the power of 14 end exponent is

  1. 130    
  2. 120    
  3. 128    
  4. 125    

The correct answer is: 120


    left parenthesis 1 plus x plus x to the power of 2 end exponent plus x to the power of 3 end exponent right parenthesis to the power of 6 end exponent equals open parentheses 1 plus x close parentheses to the power of 6 end exponent open parentheses 1 plus x to the power of 2 end exponent close parentheses to the power of 6 end exponent
    equals open parentheses blank to the power of 6 end exponent C subscript 0 end subscript plus blank to the power of 6 end exponent C subscript 1 end subscript x plus blank to the power of 6 end exponent C subscript 2 end subscript x to the power of 2 end exponent plus blank to the power of 6 end exponent C subscript 3 end subscript x to the power of 3 end exponent plus blank to the power of 6 end exponent C subscript 4 end subscript x to the power of 4 end exponent plus blank to the power of 6 end exponent C subscript 5 end subscript x to the power of 5 end exponent plus blank to the power of 6 end exponent C subscript 6 end subscript x to the power of 6 end exponent close parentheses cross times left parenthesis blank to the power of 6 end exponent C subscript 0 end subscript plus blank to the power of 6 end exponent C subscript 1 end subscript x to the power of 2 end exponent plus blank to the power of 6 end exponent C subscript 2 end subscript x to the power of 4 end exponent plus
    blank to the power of 6 end exponent C subscript 3 end subscript x to the power of 6 end exponent plus blank to the power of 6 end exponent C subscript 4 end subscript x to the power of 8 end exponent plus blank to the power of 6 end exponent C subscript 5 end subscript x to the power of 10 end exponent plus blank to the power of 6 end exponent C subscript 6 end subscript x to the power of 12 end exponent right parenthesis
    therefore Coefficient of x to the power of 14 end exponent in left parenthesis 1 plus x plus x to the power of 2 end exponent plus x to the power of 3 end exponent right parenthesis to the power of 6 end exponent
    equals blank to the power of 6 end exponent C subscript 2 end subscript bullet blank to the power of 6 end exponent C subscript 6 end subscript plus blank to the power of 6 end exponent C subscript 4 end subscript bullet blank to the power of 6 end exponent C subscript 5 end subscript plus blank to the power of 6 end exponent C subscript 6 end subscript bullet blank to the power of 6 end exponent C subscript 4 end subscript
    equals 15 plus 90 plus 15 equals 120

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