a: \(\dfrac{7x-y}{x+y}-\dfrac{6x+y}{x+y}\)(ĐKXĐ: x<>-y)
\(=\dfrac{7x-y-6x-y}{x+y}\)
\(=\dfrac{x-2y}{x+y}\)
b:
\(\dfrac{x}{x-4}-\dfrac{16}{x^2-4x}\)(ĐKXĐ: \(x\notin\left\{0;4\right\}\))
\(=\dfrac{x^2-16}{x\left(x-4\right)}\)
\(=\dfrac{\left(x-4\right)\left(x+4\right)}{x\left(x-4\right)}=\dfrac{x+4}{x}\)