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4+8+12...52-2-7-10-......50= va rog!! Dau 40p

Răspuns :

4+4×2+4×3+4×4+...+4×13-2-7-10-...-40=
4-2+4×2-7+4×3-10...-40=
2+1+2+3+4+5+6+7+8+9+10+11+12=
2+(13×12÷2)=2+78=80