1/(x-1)(x-2)+1/(x-2)(x-3)+1/(x-3)(x-4)+1/(x-4)(x-5)= 1/(x^2-2x-x+2)+1/(x^2-3x-2x+6)+1/(x^2-4x-3x+12)+1/x^2-5x-4x+20)=1/(x^2-3x+2)+1/(x^2-5x+6)+1/(x^2-7x+12)+1/x^2-9x+20)=4/(x^2-3x+2)+(x^2-5x+6)+(x^2-7x+12)+(x^2-9x+20)=4/(4x^2-24x+40)=1/(x^2-6x+10) кажется так
