Question

rút gọn

\(A=\dfrac{3}{x+3}+\dfrac{1}{x-3}-\dfrac{18}{9-x^2}\)

Answer 1

\(\Leftrightarrow A=\dfrac{3}{x+3}+\dfrac{1}{x-3}-\dfrac{18}{\left(3-x\right)\left(3+x\right)}\)

\(\Leftrightarrow A=\dfrac{3}{x+3}+\dfrac{1}{x-3}+\dfrac{18}{\left(x-3\right)\left(x+3\right)}\)

\(\Leftrightarrow A=\dfrac{3x-9+x+3+18}{\left(x+3\right)\left(x-3\right)}=\dfrac{4x+12}{\left(x+3\right)\left(x-3\right)}\)

\(\Leftrightarrow A=\dfrac{4\left(x+3\right)}{\left(x+3\right)\left(x-3\right)}=\dfrac{4}{x-3}\)