Môn Toán Lớp 6: a=2+2^2+2^3+2^4+…….+2^2017

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A = 2+2^2+2^3+2^4+…….+2^2017

=> 2A = 2^2+2^3+2^4+ 2^5 + …….+2^2018

=> 2A – A = (2^2+2^3+2^4+ 2^5 + …….+2^2018) – (2+2^2+2^3+2^4+…….+2^2017)

=> A = 2^2+2^3+2^4+ 2^5 + …….+2^2018 – 2-2^2-2^3-2^4-…….-2^2017

=> A = 2^2018 – 2

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