a: \(=\dfrac{x-2+x+1}{2x-1}=\dfrac{2x-1}{2x-1}=1\)
b: \(=\dfrac{-9x^2-3x+6x^2-2x}{\left(3x+1\right)\left(3x-1\right)}\cdot\dfrac{\left(3x-1\right)^2}{2x\left(3x+5\right)}\)
\(=\dfrac{-x\left(3x+5\right)}{\left(3x+1\right)\cdot2x\cdot\left(3x+5\right)}\cdot\left(3x-1\right)=\dfrac{-\left(3x-1\right)}{2\left(3x+1\right)}\)