a) ĐKXĐ:
\(x^2-1\ne0\Leftrightarrow x\ne\pm1\)
b) \(A=\dfrac{x^2-2x+1}{x^2-1}\)
\(A=\dfrac{x^2-2\cdot x\cdot1+1^2}{x^2-1^2}\)
\(A=\dfrac{\left(x-1\right)^2}{\left(x+1\right)\left(x-1\right)}\)
\(A=\dfrac{x-1}{x+1}\)
c) Thay x = 3 vào A ta có:
\(A=\dfrac{3-1}{3+1}=\dfrac{2}{4}=\dfrac{1}{2}\)
a) ĐKXĐ:
\(9x^2-y^2\ne0\Leftrightarrow\left(3x\right)^2-y^2\ne0\Leftrightarrow\left(3x-y\right)\left(3x+y\right)\ne0\)
\(\Leftrightarrow3x\ne\pm y\)
b) \(B=\dfrac{6x-2y}{9x^2-y^2}\)
\(B=\dfrac{2\cdot3x-2y}{\left(3x\right)^2-y^2}\)
\(B=\dfrac{2\left(3x-y\right)}{\left(3x+y\right)\left(3x-y\right)}\)
\(B=\dfrac{2}{3x+y}\)
Thay x = 1 và \(y=\dfrac{1}{2}\) và B ta có:
\(B=\dfrac{2}{3\cdot1+\dfrac{1}{2}}=\dfrac{2}{3+\dfrac{1}{2}}=\dfrac{2}{\dfrac{7}{2}}=\dfrac{4}{7}\)
