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a fost răspuns

calculati : 1+4+7+.....+91 va roog
S₂=5¹+5²+5³+.....+5¹⁰
urgent !!!!!

Răspuns :

Vilmaristul
aflam numarul de termeni: (91-1):3+1=31
suma gauss: (31*92):2=31*46=1426
S₂=5¹+5²+...........+5¹⁰| x5
5S₂=5²+5³+.......+5¹⁰+5¹¹
5S₂-S₂=5²+5³+......+5¹⁰+5¹¹-5-5²-5³-........-5¹⁰
4S₂=5¹¹-5
S2=5(5¹⁰-1)/4