If x is small so that x2 and higher powers can be neglected, then the approximate value for (1−2x)−1(1−3x)−2(1−4x)−3 is
1-2x
1-3x
1-4x
1-5x
(1−2x)−1(1−3x)−2(1−4x)−3=(1+2x)(1+6x)(1−12x)==(1+2x+6x−12x)=1−4x