Question

Calculati 1+2+3+......n=210 ....va multumesc

Answer 1

1+2+3+...+n=210
⇒n[n+1]/2=210
⇒n[n+1]=2·210
⇒n[n+1]=420
⇒n=20 ,deoarece 20[20+1]⇒20·21=420;

Answer 2

1+2+3+...n=210
n*(n+1)\2=210
n*(n+1)=420
n=20  deoarece  20*21=420
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