Basic Angles / Reference angles   Using your calculator, determine what is sin 30°, sin 150°, sin 210° and sin 330°?   sin 30° = 0.5  sin 150° = 0.5  sin 210°= -0.5  sin 330°= -0.5   What do you think is the relationship between these angles ?   30° = 30°                (1st quadrant )  150° = 180° – 30°       (2nd quadrant)  210° = 180° + 30°       (3rd quadrant)  330° = 360° – 330°     (4th quadrant)   You would realise that sine is positive in the 1st and 2nd qudrants   You can carry out the same exercise with cos and tan  cosine is positive in the 1st and 4th quadrant  tangent is positive in the 1st and 3rd quadrant                We can use the diagram above to help us remember which functions are positive in the quadrants   A means all the functions are positive in 1st quadrant  T means that only tangent is positive in the 3rd quadrant   I remember this as All Science Teachers are Charming    Example 1  Given that for x between and   Determine the value of  a) sin x  b) sin 2x ...