a,
Điều kiện: $\begin{cases}x\ne-2\\x\ne-3\\x\ne -\dfrac74\end{cases}$
`B=1/((x+2)(x+3))+1/(x+3)+1/(4x^2+15x+14)`
`=1/((x+2)(x+3))+1/(x+3)+1/((4x+7)(x+2))`
`=(4x+7)/((x+2)(x+3)(4x+7))+((x+2)(4x+7))/((x+2)(x+3)(4x+7))+(x+3)/((x+2)(x+3)(4x+7))`
`=(4x+7+4x^2+15x+14+x+3)/((x+2)(x+3)(4x+7))`
`=(4x^2+20x+24)/((x+2)(x+3)(4x+7))`
`=(4(x+2)(x+3))/((x+2)(x+3)(4x+7))`
`=4/(4x+7)`
b,
`B<0`
`↔4/(4x+7)<0`
Vì `4>0`
`→4x+7<0`
`→x<-7/4`