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Alexandrapopesvu39
a fost răspuns

calculați sumele :1+2+3+......+20;1+2+3+.....+100;2+4+6+....+100;1+3+5+.....+21;1+4+7+10+....37;5+10+15...+100=​

Răspuns :

Suzana2suzana

Răspuns:

Explicație pas cu pas:

1+2+3+......+20=20·21/2=10·21=210

1+2+3+.....+100=100·101/2=50·101=5050

2+4+6+....+100=2(1+2+...+50)=2·50·51/2=50·51=255

1+3+5+.....+21=2+4+....+22-11=2(1+2+...+11) -11=2·11·12/2-11=11·12-11=11²=121

1+4+7+10+....37=3+6+9.....+39-2·13=3(1+2+...+39)-26=3·39·40/2-26=

=3·39·20-26=2340-26==2314

5+10+15...+100=5(1+2+....+20)=5·20·21/2=5·10·21=1050

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