If sin(3x) = cos(3x), then it implies 3x = 90° - 3x + k*360°, or 3x + 3x = 90° + k*360° 6x = 90° + k*360°. Giving "k" the values k= 0, 1, 2, 3, 4, 5, you get 6 (six) values for x in the given interval x = 15°, 75°, 135°, 195°, 255°, 315°. ANSWER