You can express the sine, cosine or tangent of any number as the sum of an infinite series. Generally, the sum will be an irrational number. In real-life applications, we approximate the values to whatever number of digits are needed. There is a method that will tell us how many terms in the infinite series we must evaluate in order to reach a particular level of accuracy. You will learn about this when you take calculus. In the meanwhile, I wouldn't worry about it. Your calculator or CAS will evaluate any trig functions you need evaluated.