Denisaalesiaask
a fost răspuns

Calculati :

a) 3+6+9+12+...+2019
b) 4+8+12+...+2020
c) 5+10+15+20+...+2020
d) 7+14+21+...+2023​

Răspuns :

3+6+2+12+...+2019=3(1+2+3+...+673)=3(673×674)÷2=3×(673×337)=3×226801=680403
4+8+12+...+2020=4(1+2+3+...+505)=4×(505×506)÷2=2×255530=511060
5+10+15+ 20+...+2020=5(1+2+3+4+...404)=5×(404×405)÷2=5×163620÷2=818100÷2=409050
7+14+21+...+2023=7(1+2+3+...+289)=7×(289×290)÷2=7×83810÷2=586670÷2=293335
Norisordulceask

a)3(1+2+3+...+673)=3[(673×674)÷2]=680403

b)4(1+2+3+...+505)=4[(505×506)÷2]=511060

c)5(1+2+3+...+404)=5[(404×405)÷2]=409050

d)7(1+2+3+...+289)=7[(289×290)÷2]=293335

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