`***`Lời giải`***`
ĐKXĐ:$\begin{cases} x^2-x-6\neq0\\3x^2-4x-15\neq0\\3x^2+11x+10\neq0 \\\end{cases}$ `<=>`$\begin{cases} (x-3)(x+2)\neq0\\(x-3)(3x+5)\neq0\\(x+2)(3x+5)\neq0\\ \end{cases}$ `=>`$\begin{cases} x-3\neq0\\3x+5\neq0\\x+2\neq0\ \end{cases}$ `<=>`$\begin{cases} x\neq3\\3x\neq-5\\x\neq-2\end{cases}$ `<=>`$\begin{cases} x\neq3\\x\neq-5/3\\x\neq-2 \end{cases}$
`B=(\frac{x}{x^2-x-6}-\frac{x-1}{3x^2-4x-15}):\frac{x^4-2x^2+1}{3x^2+11x+10}.(x^2-2x+1)`
`=(\frac{x}{x^2-3x+2x-6}-\frac{x-1}{3x^2+5x-9x-15}):\frac{x^4-2x^2+1}{3x^2+6x+5x+10}.(x^2-2x+1)`
`=(\frac{x}{x(x-3)+2(x-3)}-\frac{x-1}{3x(x-3)+5(x-3)}):\frac{x^4-2x^2+1}{3x(x+2)+5(x+2)}.(x-1)^2`
`=(\frac{x}{(x-3)(x+2)}-\frac{x-1}{(x-3)(3x+5)}):\frac{x^4-2x^2+1}{(x+2)(3x+5)}.(x-1)^2`
`=\frac{x(3x+5)-(x-1)(x+2)}{(x-3)(x+2)(3x+5)}:\frac{x^4-2x^2+1}{(x+2)(3x+5)}.(x-1)^2`
`=\frac{3x^2+5x-x^2-2x+x+2}{(x-3)(x+2)(3x+5)}:\frac{x^4-2x^2+1}{(x+2)(3x+5)}.(x-1)^2`
`=\frac{2x^2+4x+2}{(x-3)(x+2)(3x+5)}:\frac{x^4-2x^2+1}{(x+2)(3x+5)}.(x-1)^2`
`=\frac{2x^2+4x+2}{(x-3)(x+2)(3x+5)}.\frac{(x+2)(3x+5)}{ x^4-2x^2+1}.(x-1)^2`
`=\frac{(2x^2+4x+2)(x-1)^2}{(x-3)( x^4-2x^2+1)}`
`=\frac{2(x^2+2x+1)(x-1)^2}{(x-3)( x^2-2x+1)(x^2+2x+1)}`
`=\frac{2(x+1)^2(x-1)^2}{(x-3)( x-1)^2(x+1)^2}`
`=\frac{2}{x-3}`
