The best way to think about this value is to picture the graph of the "normal" sin wave. One period starts at (0, 0), goes up to a y value of 1 at an x value of [tex] \frac{ \pi }{2} [/tex], goes back down to a y value of 0 at x = [tex] \pi [/tex], goes down to a y value of -1 at x = [tex] \frac{3 \pi }{2} [/tex] and ends up completing one period at a y value of 0 and an x value of [tex]2 \pi [/tex]. We can see from that what the sin ratios are at each one of those x values. When x = 0, y = 0, so the sin of 0 is 0. Check your calculator to see that this is true, but understanding the graph tells you WHY it is true.
