高校数学の質問スレ Part419

1/(x+1)/(x+2)+1/(x+2)/(x+3)=k
(x+3)+(x+1)=k(x+1)(x+2)(x+3)
1/k=(x+1)(x+2)(x+3)/(2*(x+2))
2/k=(x+1)(x+3)
x^2+4x+3-2/k=0
判別式=4-(3-2/k)=1+2/k>0
k^2+2k=k(k+2)>0
k<-2または0<k