1) 6х(х - а) /х^4(a - x) =- 6(x - a)/x^3(x - a) = -6/x^3
2) (4x - 48)/(12y - xy) = 4(x - 12)/y(12 - x) = -4(12 - x)/y(12 - x)= -4/у
3) (y^6 - y^2)/(y^4 - y^2) = y^2(y^4 -1)/y^2(y^2 -1) = (y^4 -1)/(y^2 -1)=
=(y^2-1)(y^2+1)/(y^2-1) = y^2 +1
4)11/(x^2 -64) + (x - 3)/(x^2 -64) = (11 + x - 3)/(x^2 -64) =(8 + x)/(x^2 - 64)=
=(8 +x)/(x - 8)(x + 8)= 1/(x - 8)