S=n(a1+an):2
23=21(a1+16):2
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46=21a1 + 336
21a1 = 46 - 336 = - 290
a1= -290:21= 13 intregi si 17/21
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a21=a1+20r
16= -290/21 +20r
16x21 + 290 = 20x21r
336+290 = 42r
42r=626
r=626:42 = 14 si 38/42 = 14 intregi si 19/21
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Nu ma asteptam sa dea rezultate fractionare, dar asta este, daca nu ai gresit cumva in enunt.
Oricum, ai de invatat de aici procedeul de calcul.
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Succes in continuare!
