For the period you should be able to derive it from the unit circle definitions using congruency testing. This will help you know whether function is odd or even. I recommend knowing what sin, cos, tan look like. You will need to know the definition of period, odd/even functions. Sec(theta) = 1/cos(theta) # third letter of secant is cĬot(theta) = 1/tan(theta) # third letter of cotangent is t Using the unit circle definition (see above) you will end up with cos^2(theta)+sin^2(theta)=1 from direct substitution.įor reciprocal identities observe the third letter of cosecant, cotangent, secant.Ĭosec(theta) = 1/sin(theta) # third letter of cosecant is s The pythagorean identities come from equation of the circle The complementary angle identities can be proven by proving they hold for each quadrant than making use of the period to prove they hold for all real numbers. There are some other memory tricks you can use.Ĭo is a prefix the stands for complementary. To add to the article, the unit circle definitions of the trigonometric function are important namely: Pretty much all the identities are important in some way. There is always the risk a memory pathway in your brain could change without you realising. Ideally speaking you would have reference sheet you could use.