15 points Order the following numbers from least to greatest. $\frac{-\pi}{2},-1 \frac{1}{3},-\sqrt{2}$ \[ \begin{array}{l} \frac{-\Pi}{2},-\sqrt{2},-1 \frac{1}{3} \\ -\sqrt{2}, \frac{-\Pi}{2},-1 \frac{1}{3} \end{array} \]

Step 1 ：We need to compare the three numbers \(-\frac{\pi}{2}\), \(-1 \frac{1}{3}\), and \(-\sqrt{2}\) to order them from least to greatest. Since all of them are negative, the number with the greatest absolute value will be the least.

Step 2 ：We know that \(\pi\) is approximately 3.14, so \(-\frac{\pi}{2}\) is approximately -1.57.

Step 3 ：\(-1 \frac{1}{3}\) is -1.33.

Step 4 ：\(-\sqrt{2}\) is approximately -1.41.

Step 5 ：So, we can see that \(-\frac{\pi}{2}\) is the smallest, followed by \(-\sqrt{2}\), and then \(-1 \frac{1}{3}\).

Step 6 ：\(\boxed{\text{The numbers in order from least to greatest are } -\frac{\pi}{2}, -\sqrt{2}, \text{ and } -1 \frac{1}{3}}\)