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Determina nr nat x,stiind ca x+2xX+3xX+.....+10xX=385

Răspuns :

x+2x+3x+....+10x=385
x*(1+2+3+....+10)=385
x*10*11:2=385
x*5*11=385
55x=385
x=385:55
x=7
x+2x+3x+4x+5x+6x+7x+8x+9x+10x=385
3x+7x+11x+15x+19x=385
10x+26x+19x=385
36x+19x=385
55x=385
x=385:55
x=7