a: \(\left(x-5\right)^6=\left(x-5\right)^4\)
\(\Leftrightarrow\left(x-5\right)^4\cdot\left[\left(x-5\right)^2-1\right]=0\)
\(\Leftrightarrow\left(x-5\right)^4\cdot\left(x-4\right)\left(x-6\right)=0\)
hay \(x\in\left\{5;4;6\right\}\)
b: \(\left(2x-15\right)^5=\left(2x-15\right)^3\)
\(\Leftrightarrow\left(2x-15\right)^3\left(2x-16\right)\left(2x-14\right)=0\)
hay \(x\in\left\{\dfrac{15}{2};8;7\right\}\)