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APEX Calculus

Section B.3 Trigonometry Reference

The Unit Circle.

Subsection B.3.1 Definitions of the Trigonometric Functions

Unit Circle Definition.

\(\sin(\theta) = y\) \(\cos(\theta) = x\)
\(\ds\csc(\theta) = \frac1y\) \(\ds\sec(\theta) = \frac1x\)
\(\ds\tan(\theta) = \frac yx\) \(\ds\cot(\theta) = \frac xy\)

Right Triangle Definition.

\(\ds\sin(\theta) = \frac{\text{O} }{\text{H} }\) \(\ds\csc(\theta) = \frac{\text{H} }{\text{O} }\)
\(\ds\cos(\theta) = \frac{\text{A} }{\text{H} }\) \(\ds\sec(\theta) = \frac{\text{H} }{\text{A} }\)
\(\ds\tan(\theta) = \frac{\text{O} }{\text{A} }\) \(\ds\cot(\theta) = \frac{\text{A} }{\text{O} }\)

Subsection B.3.2 Common Trigonometric Identities

  1. \(\displaystyle \sin^2(x)+\cos^2(x)= 1\)
  2. \(\displaystyle \tan^2(x)+ 1 = \sec^2(x)\)
  3. \(\displaystyle 1 + \cot^2(x)=\csc^2(x)\)
List B.3.1. Pythagorean Identities
  1. \(\displaystyle \sin(2x) = 2\sin(x)\cos(x)\)
  2. \begin{align*} \cos(2x) \amp = \cos^2(x) - \sin^2(x) \amp \amp \\ \amp = 2\cos^2(x)-1 \amp \amp \\ \amp = 1-2\sin^2(x) \amp \amp \end{align*}
  3. \(\displaystyle \tan(2x) = \frac{2\tan(x)}{1-\tan^2(x)}\)
List B.3.2. Double Angle Formulas
  1. \(\displaystyle \sin\left(\frac{\pi}{2}-x\right) = \cos(x)\)
  2. \(\displaystyle \cos\left(\frac{\pi}{2}-x\right) = \sin(x)\)
  3. \(\displaystyle \tan\left(\frac{\pi}{2}-x\right) = \cot(x)\)
  4. \(\displaystyle \csc\left(\frac{\pi}{2}-x\right) = \sec(x)\)
  5. \(\displaystyle \sec\left(\frac{\pi}{2}-x\right) = \csc(x)\)
  6. \(\displaystyle \cot\left(\frac{\pi}{2}-x\right) = \tan(x)\)
List B.3.3. Cofunction Identities
  1. \(\displaystyle \sin(-x) = -\sin(x)\)
  2. \(\displaystyle \cos (-x) = \cos(x)\)
  3. \(\displaystyle \tan (-x) = -\tan(x)\)
  4. \(\displaystyle \csc(-x) = -\csc(x)\)
  5. \(\displaystyle \sec (-x) = \sec(x)\)
  6. \(\displaystyle \cot (-x) = -\cot(x)\)
List B.3.4. Even/Odd Identities
  1. \(\displaystyle \sin^2(x) = \frac{1-\cos(2x)}{2}\)
  2. \(\displaystyle \cos^2(x) = \frac{1+\cos(2x)}{2}\)
  3. \(\displaystyle \tan^2(x) = \frac{1-\cos(2x)}{1+\cos(2x)}\)
List B.3.5. Power-Reducing Formulas
  1. \(\displaystyle \sin(x)+\sin(y) = 2\sin\left(\frac{x+y}2\right)\cos\left(\frac{x-y}2\right)\)
  2. \(\displaystyle \sin(x)-\sin(y) = 2\sin\left(\frac{x-y}2\right)\cos\left(\frac{x+y}2\right)\)
  3. \(\displaystyle \cos(x)+\cos(y) = 2\cos\left(\frac{x+y}2\right)\cos\left(\frac{x-y}2\right)\)
  4. \(\displaystyle \cos(x)-\cos(y) = -2\sin\left(\frac{x+y}2\right)\sin\left(\frac{x-y}2\right)\)
List B.3.6. Sum to Product Formulas
List B.3.7. Product to Sum Formulas
  1. \(\displaystyle \sin(x)\sin(y) = \frac12 \big(\cos(x-y) - \cos (x+y)\big)\)
  2. \(\displaystyle \cos(x)\cos(y) = \frac12\big(\cos (x-y) +\cos (x+y)\big)\)
  3. \(\displaystyle \sin(x)\cos(y) = \frac12 \big(\sin(x+y) + \sin (x-y)\big)\)
List B.3.8. Angle Sum/Difference Formulas
  1. \(\displaystyle \sin (x\pm y) = \sin(x)\cos(y) \pm \cos(x)\sin(y)\)
  2. \(\displaystyle \cos (x\pm y) = \cos(x)\cos(y) \mp \sin(x)\sin(y)\)
  3. \(\displaystyle \tan (x\pm y) = \frac{\tan(x)\pm \tan(y)}{1\mp \tan(x)\tan(y)}\)