The above shows a unit circle and the angle h shrinking to 0.
The length of the red arc is h measured in radians
The length of the blue vertical line is sin(h)
As h goes to zero it can be seen
sin(h) and h become closer and closer to the same length.
The limit as h approaches 0 of sin(h)/h = 1.
Other trigonometry pages by Hop:
What is sine and cosine?
Measuring an angle in radians, generating a sine wave
sin(a+b) and cos(a+b)
Hop's gallery, please check out my art.