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Calculati:
a)lg[tex] \frac{2}{5} [/tex]+lg[tex] \frac{5}{6} [/tex]+lg[tex] \frac{6}{7} [/tex]-lg[tex] \frac{20}{7} [/tex]=



Răspuns :

[tex]lg(\frac{2}{\not5}*\frac{\not5}{\not6}*\frac{\not6}{7}:\frac{20}{7})= \\\\= lg(\frac{\not2}{\not7}*\frac{\not7}{\not20})= \\\\ =lg \ \frac{1}{10}= lg \ 10^{-1} \to \boxed{-1}[/tex]