1. (a) How to memorize the trigonometric identities? Trigonometric Identities Easy Memory Tips: Quadrant  is acute sin cos tan IIIII IV I sin  -  -   cos  -  -   tan  -   -  sin  sin cos  cos tan  tan 180 o -  180 o +  360 o +  360 o -  TC SA Only sin is +ve Only tan is +ve Only cos is +ve All ratio are +ve Convert the trigonometric ratios with the 6. More about Trigonometry The symbol of sine/cosine/tangent remains unchanged. Write the angle as . According to the quadrant that the angle lies in, determine the sign of the trigonometric ratio. angles 180 o ±  and 360 o ± .

2. Quadrant  is obtuse sin cos tan III IIIIVIV 90 o -  90 o +  270 o +  270 o -  sin - -  cos - - -- sin  cos cos  sin tan             6. More about Trigonometry (a) How to memorize the trigonometric identities? Trigonometric Identities Easy Memory Tips: Only sin is +ve Only tan is +ve Only cos is +ve All ratio are +ve TC SA Convert the trigonometric ratios with the angles 90 o ±  and 270 o ± . The symbol of sine/cosine/tangent is changed. Write the angle as . According to the quadrant that the angle lies in, determine the sign of the trigonometric ratio.

3. Solve the equation sin  = - 0.5. (Use calculator to calculate the answer) ∵ sin  < 0 (b) For 0 o ≤  ≤360 o, how to solve the trigonometric equations?E.g. ∴  lies in quadrants III or IV Consider sin  = 0.5 first.  = 30 o ++ -- TC SA 180 o +  360 o -  ∵ The symbol of sine does not change ∴ We only need to consider 180 o +  and 360 o -  i.e.  = 180 o +  or  = 360 o -  = 210 o 30 o or = 330 o AllSin 6. More about Trigonometry