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3^x+3^x-1+3^x-2+3^x-3=40

Răspuns :

3^x+3^x-1+3^x-2+3^x-3=40
3^x ×(3^0+3^-1+3^-2+3^-3)=40
3^x ×(1+1/3+1/3^2+1/3^3)=40
3^x ×(1+1/3+1/9+1/27)=40
3^x ×(27+9+3+1)/27=40
3^x×40/27=40
3^x=27
3^x=3^3
x=3