IT100 Session 9: Trigonomic Functions
1 Nov 2017
\[ \large\begin{array}{rrcll} cosine: & \cos\ \theta &=&{x \over r} & = {1\over\sec\ \theta}\\ sine: & \sin\ \theta &=&{y \over r} & = {1\over \csc\ \theta}\\\ tangent: & \tan\ \theta &=& {y \over x} & = {1\over \cot\ \theta}\\ secant: & \sec\ \theta &=& {r \over x} & = {1\over \cos\ \theta} \\ cosecant: &\csc\ \theta &=& {r \over y} & {1 \over \sin\ \theta}\\ cotangent: &\cot\ \theta &=& {y \over x}& {1 \over \tan\ \theta}\\ \end{array} \]
\[ \large\begin{array}{rcl} \sin\theta &=& \cos\left({\pi\over 2} - \theta\right) \\ \\ \cos\theta &=& \sin\left({\pi\over 2} - \theta\right) \\ \\ \tan\theta &=& \cot\left({\pi\over 2} - \theta\right) \\ \end{array} \]
\[ \large\begin{array}{rcl} \sin\left({\theta\over 2}\right) & = & \pm \sqrt{1- \cos(\theta)\over 2}\\ \\ \cos\left({\theta\over 2}\right) & = & \pm \sqrt{1 + \cos(\theta)\over 2}\\ \\ \tan\left({\theta\over 2}\right) & = & \pm \sqrt{1 - \cos(\theta)\over 1 + \cos(\theta)} = {\sin(\theta) \over 1 + cos(\theta)} = {1 - cos(\theta)\over \sin(\theta)}\\ \end{array} \]
\[ \large\begin{array}{rcl} \sin\left(2\theta\right) & = & 2 \sin(\theta) \cos(\theta)\\ \\ \cos\left(2\theta\right) & = & \cos^2(\theta) - \sin^2(\theta) = 1 - 2 \sin^2(\theta) = 2 \cos^2(\theta) - 1\\ \\ \tan\left(2\theta\right) & = & {2 \tan(\theta)\over 1 - \tan^2(\theta)} \\ \end{array} \]
\[ \large\begin{array}{rcl} \sin^2 \theta & = & {1 - \cos(2\theta)\over 2}\\ \\ \cos^2 \theta & = & {1 + \cos(2\theta)\over 2}\\ \\ \tan^2 \theta & = & {1 - \cos(2\theta)\over 1 + \cos(2\theta)}\\ \end{array} \]
\[ \large\begin{array}{rcl} \sin(\alpha + \beta) & = & \sin\alpha \cos\beta + \cos\alpha \sin\beta\\ \\ \cos(\alpha + \beta) & = & \cos\alpha \cos\beta - \sin\alpha \sin\beta\\ \\ \tan(\alpha + \beta) & = & {\tan\alpha + \tan\beta\over 1 - \tan\alpha \tan\beta}\\ \end{array} \]
Difference \[ \large\begin{array}{rcl} \sin(\alpha - \beta) & = & \sin\alpha \cos\beta - \cos\alpha \sin\beta\\ \\ \cos(\alpha - \beta) & = & \cos\alpha \cos\beta + \sin\alpha \sin\beta\\ \\ \tan(\alpha - \beta) & = & {\tan\alpha - \tan\beta\over 1 + \tan\alpha \tan\beta}\\ \end{array} \]
\[ \large\begin{array}{rcl} \cos\alpha \cos \beta & = & {\cos(\alpha -\beta) + \cos(\alpha + \beta)\over 2}\\ \\ \sin\alpha \sin \beta & = & {\cos(\alpha -\beta) - \cos(\alpha + \beta)\over 2}\\ \\ \sin\alpha \cos \beta & = & {\sin(\alpha +\beta) + \sin(\alpha - \beta)\over 2}\\ \\ \cos\alpha \sin \beta & = & {\sin(\alpha +\beta) - \sin(\alpha - \beta)\over 2}\\ \end{array} \]
\[ \large {\sin \alpha\over a} = {\sin \beta\over b} = {\sin \gamma \over c} \]
\[ \large {a \over \sin \alpha} = {b \over \sin \beta} = {c \over \sin \gamma} \]
\[ \large Area = {bc\ \sin \alpha\over 2} = {ac\ \sin \beta\over 2} = {ab\ \sin \gamma\over 2} \]
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