Evaluate the following trigonometric function at the quadrantal angle, or state that the expression is undefined. \( \tan 0 \)

The value of \( \tan 0 \) is 0. This is because tangent is defined as the ratio of sine to cosine, and at 0 degrees (or 0 radians), \(\sin(0) = 0\) and \(\cos(0) = 1\). So, \(\tan(0) = \frac{\sin(0)}{\cos(0)} = \frac{0}{1} = 0\). Additionally, quadrantal angles—like 0, 90, 180, and 270 degrees—are key points on the unit circle where certain trigonometric values are easily observed. Knowing these can help with quick calculations in trigonometry, making it easier to solve more complex problems later!