Trig Identities You Must Know
1.. |
sin2 x + cos2 x = 1 tan2 x + 1 = sec2 x |
2. |
cos 2x = cos2 x - sin2 x = 1 - 2 sin2 x = 2 cos2 x - 1 sin 2x = 2 sin x cos x |
3. |
cos (x + y) = cos x cos y - sin x sin y cos (x - y) = cos x cos y + sin x sin y sin (x + y) = sin x cos y + cos x sin y sin (x - y) = sin x cos y - cos x sin y |
4. |
Notice you could add and subtract the formulas above to obtain the following: cos x cos y = ½ [cos (x + y) + cos (x – y)] sin x sin y = ½ [cos (x – y) – cos (x + y)] sin x cos y = ½ [sin (x – y) + sin (x + y)] |
5. |
cos2 x = (1
+ cos 2x)/2 sin2 x =
(1 - cos 2x)/2 |
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