a: \(A=\dfrac{x\left(x^2-5x+6\right)}{-\left(4x^2-10x+4\right)}\)
\(=\dfrac{-x\left(x-2\right)\left(x-3\right)}{4x^2-8x-2x+4}\)
\(=\dfrac{-x\left(x-2\right)\left(x-3\right)}{\left(x-2\right)\left(4x-2\right)}=\dfrac{-x\left(x-3\right)}{4x-2}\)
b: \(=\dfrac{5\left(x-3\right)}{\left(x-3\right)\left(x-1\right)}=\dfrac{5}{x-1}\)
c: \(=\dfrac{\left(x+2\right)\left(x+3\right)}{\left(x+2\right)^2}=\dfrac{x+3}{x+2}\)