Suppose that $\theta$ is an angle in standard position whose terminal side intersects the unit circle at $\left(-\frac{21}{29},-\frac{20}{29}\right)$. Find the exact values of $\sin \theta, \sec \theta$, and $\tan \theta$. \[ \begin{array}{l} \sin \theta=\square \\ \sec \theta=\square \\ \tan \theta=\square \end{array} \]

Step 1 ：The coordinates of the point where the terminal side of the angle intersects the unit circle are given by \((\cos \theta, \sin \theta)\). Therefore, we can directly read off the value of \(\sin \theta\) from the coordinates. So, \(\sin \theta = -\frac{20}{29}\).

Step 2 ：The value of \(\sec \theta\) is the reciprocal of \(\cos \theta\). So, \(\sec \theta = -\frac{29}{21}\).

Step 3 ：The value of \(\tan \theta\) is given by \(\frac{\sin \theta}{\cos \theta}\). So, \(\tan \theta = \frac{20}{21}\).

Step 4 ：Final Answer: \(\sin \theta=\boxed{-\frac{20}{29}}, \sec \theta=\boxed{-\frac{29}{21}}, \tan \theta=\boxed{\frac{20}{21}}\)