Răspuns:
Explicație pas cu pas:
18a)
1 + 3 + 5 + ...+ 47 = 24*(1 + 47)/2 = 24*48/2 = 24*24
1 + 3 + 5 + ...+ 23 = 12*(1 + 23)/2 = 12*24/2 = 6*24
24*24/6*24 = 4
√4 = 2
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b)
1 + 3 + 5 + ...+ 2009 + 2011 = 1006*(1 + 2011)/2 = 1006*2012/2 = 1006*1006
1 + 3 + 5 + ...+1003 + 1005 = 503*(1 + 1005)2 = 503*1006/2 = 505*503
1006*1006/503*503 = 2*2 = 4
√4 = 2