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Ena88and
a fost răspuns

Dati factor comun apoi calculati : b) 13+26+39+...×715 si c)21+42+36....+1890 si d)101+302+303+...909+1010+...+9898+9999

Răspuns :

Atdei1
b)13+26+39+....×714=13 ×(1+2+3+4+.....55)=13×55×56÷2=13×55×28=715×28=20020
c)21+42+36.....+1890=21×(1+2+3+4....90)=21×(90×91)÷2=21×8190÷2=21×4905=85995
d)101+302+303+.....909+1010+....9898+9999=(101+909)+(208+808)+(303+707)+(404+606)+505=1010+1010+1010+1010=1010×4+505=4040+505=4545

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