1/(x+1)(x+2) =1/(x+1)-1/(x+2) =1/[2+(x-1)]-1/[3+(x-1)] =1/2 ·1/[1+(x-1)/2]-1/3 ·1/[1+(x-1)/3] =1/2∑(-1)^n [(x-1)/2]^n -1/3∑(-1)^n [(x-1)/3]^n 自己思考。3575
