Jugular Expansion

( 1 + x ) 101 ( 1 + x 2 x ) 100 (1+x)^{101}(1+x^2-x)^{100}

How many terms are there when the above expression is expanded and like terms are combined?


The answer is 202.

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1 solution

Rishabh Jain
May 11, 2016

Relevant wiki: Properties of Binomial Coefficients

Write ( 1 + x ) 101 = ( 1 + x ) ( 1 + x ) 100 \small{(1+x)^{101}=(1+x)(1+x)^{100}} so that: ( 1 + x ) [ ( 1 + x ) ( 1 + x 2 x ) ] 100 \large (1+x)\left[(1+x)(1+x^2-x)\right]^{100} = ( 1 + x ) [ 1 + x 3 ] 100 \large =(1+x)\left[1+x^3\right]^{100} = [ 1 + x 3 ] 100 + x [ 1 + x 3 ] 100 \large =\left[1+x^3\right]^{\color{#D61F06}{100}}+x\left[1+x^3\right]^{\color{#D61F06}{100}}

(The first bracket will give 101 101 independent terms of the form x 3 n x^{3n} which cannot be grouped with any of the term of second bracket since they will be of the form x 3 n + 1 x^{3n+1} ( n Z + { 0 } ) ~~(n\in\mathbb{Z^+}\cup \{0\}) .)

Thus we would get a total of 101 + 101 = 202 \large 101+101=\boxed{\color{#20A900}{202}} terms.

nice solution.. +1

Sabhrant Sachan - 5 years, 1 month ago

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T h a n k s \large \mathfrak{T}hanks

Rishabh Jain - 5 years, 1 month ago

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