Let (x1, y1) and (x2, y2) be points on the unit circle corresponding to t = t1

Question:

Let (x1, y1) and (x2, y2) be points on the unit circle corresponding to t = t1 and t = π − t1, respectively.
(a) Identify the symmetry of the points (x1, y1) and(x2, y2).
(b) Make a conjecture about any relationship between sin t1 and sin(π − t1).
(c) Make a conjecture about any relationship between cos t1 and cos(π − t1).