Investigate and make a conjecture:
Try making your own GSP sketch to investigate, or just click here (requires GSP 4.0):
Try proving this conjecture on your own first, then click here to compare your efforts with this proof:
Extension: Use this theorem and the Law of Sines to deduce the "addition formula": sin(B + C) = sinBcosC + sinCcosB. Try this on your own, then compare your efforts with this.