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x+3++5x+...+25x=2x+4x=...+24x+39
VA ROG imi trebuie pana maine si nu inteleg

Răspuns :

Bunicaluiandrei
x(1+3+5+.....+25) = 2x(1+2+3+.....+12)



x(1+3+5+.......+25) = 2x(1+2+3+.....+12) +39
x[ 1+ (1+1·2)+(1+2·2)+(1+3·2)+........+(1+12·2)] = 2x·12·13/2 + 39
x[1·13 + 2(1+2+3+.......+12)] = 156x + 39
x(13+156) = 156x + 39
169x = 156x +39
13x= 39    x=3