\(a,\) Ta có : \(\left(-9\right)+\left(-15\right)=-24\)
\(\left(-10\right)+\left(-14\right)=-24\)
Vì : \(-24=-24\Rightarrow\left(-9\right)+\left(-15\right)=\left(-10\right)+\left(-14\right)\)
\(b,\) Ta có : \(\left(-19\right)+\left(-5\right)=-24\)
\(\left(-21\right)+\left(-2\right)=-23\)
Vì \(-24< -23\Rightarrow\left(-19\right)+\left(-5\right)< \left(-21\right)+\left(-2\right)\)