Giải:
a) \(25.5^{x+5}=5^8\)
\(\Leftrightarrow5^2.5^{x+5}=5^8\)
\(\Leftrightarrow5^{x+7}=5^8\)
\(\Leftrightarrow x+7=8\)
\(\Leftrightarrow x=1\)
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b) \(124+\dfrac{225}{\left(x-3\right)^2}=57\)
\(\Leftrightarrow\dfrac{15^2}{\left(x-3\right)^2}=-67\)
\(\Leftrightarrow\left(\dfrac{15}{x-3}\right)^2=-67\)
Mà \(\left(\dfrac{15}{x-3}\right)^2\ge0,\forall x\left(xe3\right)\)
Suy ra không có x thỏa mãn
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