Question

Answer 1

Lỗi ạ

Answer 2

1: ĐKXĐ: \(x\notin\left\{5;-5\right\}\)

2: \(A=\dfrac{2x-5x-25-x+5}{\left(x-5\right)\left(x+5\right)}=\dfrac{-4x+20}{\left(x-5\right)\left(x+5\right)}=\dfrac{-4}{x+5}\)

Answer 3

1: ĐKXĐ: x∉{5;-5}

2: \(A=\frac{2x}{x^2-25}-\frac{5}{x-5}-\frac{1}{x+5}\)

\(=\frac{2x}{\left(x-5\right)\left(x+5\right)}-\frac{5}{x-5}-\frac{1}{x+5}\)

\(=\frac{2x-5\left(x+5\right)-x+5}{\left(x-5\right)\left(x+5\right)}=\frac{x+5-5\left(x+5\right)}{\left(x-5\right)\left(x+5\right)}\)

\(=\frac{-4\left(x+5\right)}{\left(x-5\right)\left(x+5\right)}=\frac{-4}{x-5}\)

3: Thay x=1 vào A, ta được:

\(A=\frac{-4}{1-5}=\frac{-4}{-4}=1\)