3) [(х-2)(х-1) - 2(х^2 - 1)+3(x-2)]/(x-2)(x^2 - 1) = [x^2 - 2x-x +2 -2x^2 +2 +3x - 6]/(x-2)(x^2 - 1)= [-x^2 - 4]/(x-2)(x^2 - 1) = - (x^2 +4)/(x-2)(x^2 - 1)
4) 1 / (b - 3) -3b^2 / (b^3 - 3^3) + 3 / (b^2 + 3b + 9) = [b^2 + 3b + 9 - 3b^2 + 3b - 9] / (b - 3)(b^2 + 3b + 9) = (-2b^2 + 6b) / (b - 3) (b^2 + 3b + 9) = -2b(b - 3) / (b-3)(b^2 + 3b + 9) = -2b / (b^2 + 3b + 9) = -2 * 2.5 / (2.5^2 + 3 * 2.5 + 9) = - 5 / 22.75 = - 20/91