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CALCULATI
1+7+49+343+....+823543


Răspuns :

[tex]A=1+7+49+343+...+823543\\ A=1+7+7^2+7^3+...+7^7\\ -7A=-7-7^2-7^3-...-7^8\\ Le adunam:\\ -6A=1-7^8\\ 6A=7^8-1\\ A=\frac{7^8-1}{6}[/tex]
[tex]A=\frac{5764801-1}{6}\\ A=\frac{5764800}{6}=960800[/tex]