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a fost răspuns

Se stie ca x+2y-z = 3 . Calculati suma :
S= (x+2y-z) + (2x+4y-2z) +3x+6y-3z) +..........+(10x+20y-10z)

Răspuns :

S=(x+2y-z)+2(x+2y-z)+3(x+2y-z)+....+10(x+2y-z)=(x+2y-z)(1+2+3+...+10)=3x10(10+1)supra2=15x11=165

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