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2+4+6+.....+100=? ajutor

Răspuns :

2×(1+2+3+...+50)=
=2×[50×(50+1)÷2]=
=2×(50×51÷2)=
×2 si ÷2 se elimina =>
=2550
[100•(100+1)]:2=
(100•101):2=
10100:2=
5050