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Afla numărul natural X din egalitate:X+2xX+3xX+4xX+.........+19xX+20xX=2100

Răspuns :

X+2xX+3xX+4xX+.........+19xX+20xX=2100  se aplica formula lui Gauss
(20X*21X):2=2100
X(20*21)=2100*2
420*X=4200
X=4200:420
X=10