\(2x^2+x-6\\ =2x^2+4x-3x-6\\ =\left(2x^2+4x\right)-\left(3x+6\right)\\ =2x\left(x+2\right)-3\left(x+2\right)\\ =\left(x+2\right)\left(2x-3\right)\)

\(a.6x^3y^2.\left(2-x\right)+9x^2y^2.\left(x-2\right)\\ =6x^3y^2.\left(2-x\right)-9x^2y^2.\left(2-x\right)\\ =3x^2y^2\left(2-x\right)\left(2x-3\right)\)

\(a.1\dfrac{4}{23}+\dfrac{5}{21}-\dfrac{4}{23}+0,5+\dfrac{16}{21}\\ =\left(1\dfrac{4}{23}-\dfrac{4}{23}\right)+\left(\dfrac{5}{21}+\dfrac{16}{21}\right)+0,5\\ =1+1+0,5=2,5\)