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cakculati 1+3+5+....+89+91

Răspuns :

s=1+3+5+......+89+91
s=91+89+.....5+3+1
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2s=92+92+92......+92

(91-1):2+1= 90:2+1= 45+1=46
2s=46×92
2s=4232
s=4232:2
s= 2116