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calculati 1+3+5+...+89+91

Răspuns :

2*1-1 + 2*2-1 + ... + 2*46-1 = 2*(1+2+... +46)-46=2*47*46:2-46= 47*46-46=46*46= 2116
1+3+5...+89+91=
pas=2
(91-1):2+1=90:2+1=45+1=46
(1+91)x 46 : 2=90 x 46:2=46 : 2 x 90 =23 x 90=2070