Compute $\cos 270^\circ$.
I know that the cosine function measures the x-coordinate of a point on the unit circle that corresponds to a given angle. So, to find $\cos 270^\circ$, I need to locate the point on the unit circle that is 270 degrees counterclockwise from the positive x-axis. I can use the fact that the unit circle is divided into four quadrants, each with an angle of 90 degrees, to help me find the point. If I start from the positive x-axis and move 90 degrees counterclockwise, I reach the positive y-axis. If I move another 90 degrees counterclockwise, I reach the negative x-axis. If I move another 90 degrees counterclockwise, I reach the negative y-axis. This means that the point on the unit circle that corresponds to 270 degrees is (0, -1). Therefore, the x-coordinate of this point, which is the cosine value, is 0. 