Don't think of them in terms the full function. You can approximate a strait line by a small part of a long sine wave. http://www.wolframalpha.com/input/?i=Sin%28x%29++from+.01+to...

But, for a real world example look at jpeg.

Next, each 8×8 block of each component (Y, Cb, Cr) is converted to a frequency-___domain representation, using a normalized, two-dimensional type-II discrete cosine transform (DCT). http://en.wikipedia.org/wiki/JPEG