I'm currently learning trig identifies and on Khan academy, there is a graph demonstrating how sine and cosine addition identities are derived
I understand how each of the length is derived.
The author also mentioned
A similar diagram could show the angle difference identities. Can you draw one?
I can derive the sine and cosine angle difference identities algebraically.
Below is how I derive the sine angle difference identity. (by using the fact that
cos(-b) = cos(b) and sin(-b) = -sin(b))
But I'm not sure how to derive the sine and cosine angle difference identities graphically. Could someone please provide me with a hint?