`B = ((2x^2 + 1)/(x^3- 1) - 1/(x-1) ) : (1 - (x^2 + 4)/(x^2 + x+1))`
` = ((2x^2 + 1)/(x^3 - 1) -(x^2+ x+1)/(x^3 - 1) ) : ( (x^3 - 1)/(x^3 -1) - ((x^2+4).(x-1))/(x^3-1))`
` = ((2x^2 + 1) - (x^2 + x+1))/(x^3-1) : ((x^3 - 1) - (x^2 + 4) . (x-1))/(x^3-1)`
` = (2x^2 + 1 - x^2 - x-1)/(x^3-1) . (x^3 - 1)/((x^3 - 1) - (x^2+4).(x-1))`
` = (x^2 -x)/((x^3 - 1) - (x^2 +4).(x-1)`
` = (x.(x-1))/((x^2 + x+1).(x-1) - (x^2 + 4).(x-1))`
` = (x.(x-1))/((x-1).[(x^2 + x + 1) - (x^2 + 4)])`
` = x/(x^2 + x + 1 - x^2 - 4)`
` = x/(x-3)`
