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calculati suma:S=9+99+999+....+999...99 (2017 de 9)​

Răspuns :

S = 9+99+999+...+999...99 {2017 de 9}

S = 10+100+1000+...+1000...0 - 1-1-1-1-...-1 {de 2017 ori}

S = 10¹+10²+10³+...+10²⁰¹⁷ - 1•2017

S = 10•(10²⁰¹⁷-1)/(10-1) - 2017

S = (10²⁰¹⁸ - 10)/9 - 2017

S = (10²⁰¹⁸ - 18163)/9