f(x)=1/[(x+1)(x+2)]
=1/(x+1)-1/(x+2)
=1/(x+4-3) - 1/(x+4-2)
=1/[2-(x+4)] - 1/[3-(x+4)]
=1/2 * 1/[1-(x+4)/2] - 1/3 * [1/[1-(x+4)/3]
=1/2【1 + [(x+4)/2]^2 + [(x+4)/2] + …… 】
- 1/3【1 + [(x+4)/3]^2 + [(x+4)/3] + …… 】
整理一下即可
要求|(4+x)/2|