I'm not sure if this is what you're asking about but...

cos(0)=1

Looking at the unit circle at 0°, we see that the coordinate is at (1,0). I would recomend memorizing the coordinates of 0° or 360°, 90°, 180°, and 270°. Since cos represents the x-coordinate, this means that at (1,0) or 0°, cos(0)=1.