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calculeaza sumele : a)s=4+7+10+....+91 b)s=6+11+16+21+....+101

Răspuns :

a.3x1+1+3x2+2+3x3+1+...+3x30+1=
=3(1+2+3+...+30)+1x30=3x30x31:2+30=
=3x15x31+30 si la celalalt e aceeasi regula