In the diagram of the point moving round the circle, look at the radius joining the centre to the point. You should be able to see that the distance we have called *a*, the distance  Cotangent of a\ COT a Cosine of a\ COS a Sine of a\ SIN a a Tangent of a\ TAN a *Fig. 7 – Graphical representation of trigonometrical functions* that the point has moved round the edge of the circle, is a way of measuring the angle through which the radius has moved away from the x-axis. When *a*=π/2, the angle is **90°** (degrees).\ When *a*=π, the angle is **180°**; and so round to when *a*=2π, and the angle is **360°**. You might just as well forget about degrees, and measure the angle in terms of *a* alone: we say then that we are measuring the angle in radians. Thus π/2 radians=**90°** and so on. You must always remember that in *NextBASIC* **SIN**, **COS** and so on use *radians* and not *degrees*. To convert *degrees* to *radians*, divide by **180** and multiply by π; to convert back from *radians* to *degrees*, you divide by π and multiply by **180**. ### Exercises 1. Using the knowledge you have gained from this chapter, define a function to convert radians to degrees (this may prove very useful to you in the future). 2. In *Fig. 7* above, the function **COT** appears while it's not part of *NextBASIC's* vocabulary. Write a function that returns the value of the *cotangent* of *a* using **TAN**.