Question

Tính nhanh giá trị biểu thức tại x = 1

\(\dfrac{1}{x-4}\).\(\dfrac{x-4}{x+1}\) - \(\dfrac{x+4}{x+1}\).\(\dfrac{8}{x^2-16}\)

Answer 1

\(=\dfrac{1}{x+1}-\dfrac{8}{\left(x+1\right)\left(x-4\right)}=\dfrac{x-4-8}{\left(x+1\right)\left(x-4\right)}=\dfrac{x-12}{\left(x+1\right)\left(x-4\right)}=\dfrac{-11}{2\cdot\left(-3\right)}=\dfrac{11}{6}\)