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Dati factor comun si calculati:

10+20+30+........+900=

13+26+39+....+715=

21+42+36+.......+1890=

101+202+303+....+909+1010+....+9898+ 9999=

Răspuns :

Iarinna
a) 10+20+30+...+900= =10×1-10×2+10×3+...90×10= =10×(1+2+3+...+90)= =10×(90×91:2)= =10×(8190:2)= =10×4095= =40950
Larissaamadeus
10*(1+2+3+...+90) = 10*((90*91)/2) = 10*(45*91) = 450*91 =40950

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