前>>400
>>402
1/(x+1)(x+2)+ 1/(x+2)(x+3)=k
x+3+x+1=k(x+1)(x+2)(x+3)
2(x+2)=k(x+1)(x+2)(x+3)
2=k(x+1)(x+3)
kx^2+4kx+3k-2=0
D/4=4k^2-k(3k-2)＞0
k^2+2k＞0
(k+2)k＞0
∴ k＜-2,0＜k