(a) How to memorize the trigonometric identities?

1. S A T C 6. More about Trigonometry (a) How to memorize the trigonometric identities? Trigonometric Identities Easy MemoryTips: Convert the trigonometric ratios with the Only sin is +ve All ratio are +ve angles 180o± and 360o±. 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. Only tan is +ve Only cos is +ve II III I IV 360o- 360o+ 180o- 180o+ sinsin  - -    sin sin sin sin coscos     - cos cos - cos cos tantan - -     tan tan tan tan

2. S A tan T C 6. More about Trigonometry (a) How to memorize the trigonometric identities? Trigonometric Identities Easy MemoryTips: Convert the trigonometric ratios with the Only sin is +ve All ratio are +ve angles 90o± and 270o±. 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. Only tan is +ve Only cos is +ve I II III IV sincos 270o- 270o+ 90o- 90o+ cossin    cos - -  cos cos cos    sin  sin sin - - sin - -    

3. E.g. S A T C 6. More about Trigonometry (b) For 0o≤≤360o, how to solve the trigonometric equations? Solve the equation sin = -0.5. Consider sin=0.5 first. + + =30o (Use calculator to calculate the answer) Sin All ∵sin <0 180o+ 360o- ∴ lies in quadrants III or IV - - ∵ The symbol of sine does not change ∴ We only need to consider180o+and 360o- i.e.=180o+or=360o- 30o 30o or=330o =210o