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5+7+9+....+61 pls cat puteti de repede




Răspuns :

5+7+9+ ....+61= n²- (1+3)
an=61
2n-1=61
2n=62
n=31

5+7+9+ ....+61= n²- (1+3) = 31²- 4=961-4= 957