c, x/x-3-x/x-5=x/x-4-x/x-6

* Hướng dẫn giải

$$\begin{gathered} \frac{x}{x-3}-\frac{x}{x-5}=\frac{x}{x-4}-\frac{x}{x-6} \\ \iff \frac{x\left(x-5\right)-x\left(x-3\right)}{x^2-8x+15}=\frac{x\left(x-6\right)-x\left(x-4\right)}{x^2-10x+24} \\ \iff \frac{x^2-5x-x^2+3x}{x^2-8x+15}=\frac{x^2-6x-x^2+4x}{x^2-10x+24} \\ \iff -2x\left(\frac{1}{x^2-8x+15}-\frac{1}{x^2-10x+24}\right)=0 \\ -2x\frac{\left(9-2x\right)}{\left(x^2-8x+15\right)\left(x^2-10x+24\right)}=0 \end{gathered}$$