chứng minh lôgarit

B

buivanbao123

$ a^2+b^2=7ab \\
\leftrightarrow (a+b)^2=9ab \\
\leftrightarrow \frac{a+b}{3}=\sqrt{ab} \\
\leftrightarrow \log _c \frac{a+b}{3}=\log _c \sqrt{ab} \\
\leftrightarrow \log _c \frac{a+b}{3}=\frac{1}{2}.\log _cab \\
\leftrightarrow\log _c \frac{a+b}{3}=\frac{1}{2}(\log _ca+\log _cb) \\
$
 
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