試題詳解

8. What is the sum of all possible values of ? between 0 and 360 such that the triangle in the coordinate plane whose vertices are (cos 50°, sin 50°), (cos 70°, sin 70°), and (cos t°, sin t°) is the isosceles?
(A) 300
(B) 330
(C) 390
(D) 420