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Many digits

Author: admin
Problem has been solved: 94 times

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Let $ x = \underbrace {444 ... 4} _ \text {2020 pieces} $, $ y = - \underbrace {111 ... 1} _ \text {2020 pieces} $, $ z =\underbrace { 222 ... 2} _ \text {2020 pieces} $. Find the sum of the digits of $ x ^ 2 + 2xy + 2yz-z ^ 2-y $ in decimal.





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