Trigonometric Formulas: 

    Below are the list of all trigonometric functions formulas;

  





Basic Formulas:


 

OR

 \ csc \ left( \theta\right)\ = \ \ frac1 {\ sin\ left( \theta\right)}

=====

\ cos \ left( \theta\right) \ = \ \ frac1 {\ sec( \theta)}\

 OR

 sec \ left( \theta\right) \ = \ \ frac1 {\ cos\ left( \theta\right)}

=====


\ tan\ left( \theta\right) \ = \ \frac {\ sin\ left( \theta\right)}{\ cos\ left( \theta\right)}\

OR

\ tan\ left( \theta\right) \ = \ \frac1 {\ cot\ left( \theta\right)}

=====

\ cot\ left( \theta\right)\ = \ \ frac {\ cos\ left( \theta\right)}{\ sin \ left( \theta\right)}

OR

\ cot \ left( \theta\right) \ = \ \ frac1 {\ tan\ left( \theta\right)}

=====

\ sin^2\ left( \theta\right) \ + \ \ cos^2 \ left( \theta\right)\ = \ 1 \ 

OR

 \ sin^2\ left( \theta\right) \ = \ 1 \ - \  \ cos^2 \ left( \theta\right)

OR

 \ cos^2 \ left( \theta\right) \ = \ 1 \ - \ \ sin^2 \ left( \theta\right)

=====

 1 \ + \ \ tan^2 \ left( \theta\right) \ = \ \ sec^2 \ left( \theta\right)

OR

 \ tan^2 \ left( \theta\right) \ = \ \ sec^2 \ left(\theta\right) \ - \ 1

=====

 1 \ + \ \cot^2\ left( \theta\right) \ = \ \ csc^2 \ left(\theta\right)

OR

\ cot^2 \ left( \theta\right) \ = \ \ csc^2 \ left( \theta\right) \ - \ 1

=====

NEGATIVE(-ve) ANGLE FORMULAS:


\ sin \ left( -\theta\right) \ =\ - \ sin\ left( \theta\right)

\ cos \ left( -\theta\right) \ = \ \ cos\ left( \theta\right)

\ tan \ left( -\theta\right) \ = \ - \ tan\ left( \theta\right)

\ cot \ left( -\theta\right) \ = \ - \ cot\ left( \theta\right)  

\ sec \ left( -\theta\right) \ =\ \ sec\ left( \theta\right)

\ csc \ left( -\theta\right) \ = \ - \ csc\ left( \theta\right)


DOUBLE ANGLE FORMULAS:


 \ sin \ left( 2\theta\right) \ = \ 2 \ sin\ left( \theta\right) \ cos\ left( \theta\right)

OR

 \ sin \ left( 2\theta\right)\ = \ \ frac { 2 \tan\left( \theta\right)}{ 1\ + \ \ tan^2\ left( \theta\right)}

=====

 \ cos \ left( 2\theta\right) \ = \ \ cos^2\ left( \theta\right)\ -\ \ sin^2\ left( \theta\right)

OR

 \ cos \ left( 2\theta\right) \ = \ 2 \ cos^2 \ left( \theta\right)\ - \ 1

OR

 \ cos \ left( 2\theta\right) \ = \ 1\ - \ 2 \ sin^2\ left( \theta\right)

OR

 \ cos \ left( 2\theta\right) \ = \ \ frac {1\ - \ \ tan^2\ left( \theta\right)}{1\ + \ \ tan^2\ left( \theta\right)}

= = = = =


 \ tan \ left( 2\theta\right) \ = \ \ frac { 2 \ tan \ left( \theta\right)}{ 1-\ tan^2\ left( \theta\right)}


HALF ANGLE FORMULAS:


 \ sin \ left( \ frac \alpha2\ right) \ = \ \ pm \ sqrt{ \ frac { 1- \ cos\ left( \ alpha \ right)} 2}

 \ cos \ left( \ frac \alpha2\ right) \ = \ \ pm \ sqrt{ \ frac { 1+ \ cos\ left( \ alpha \ right)} 2}

 \ tan \ left( \ frac \alpha2\ right) \ = \ pm \ sqrt{ \ frac{1 - \ cos\ left( \ alpha \ right)} {1 + \ cos\ left( \ alpha \ right)}}


FUNDAMENTAL LAWS:


\ sin \ left( \ alpha + \ beta \ right) = \ sin\ left( \ alpha \ right) \ cos\ left( \ beta \ right) + \ cos\ left( \ alpha \ right)\ sin\ left(\ beta \ right)

\ sin\ left( \ alpha - \ beta \ right) = \ sin\ left( \ alpha \ right) \ cos\ left( \ beta \ right) - \ cos\ left( \ alpha \ right)\ sin\ left(\ beta \ right)

\ cos\ left( \ alpha + \ beta \ right) = \ cos\ left( \ alpha \ right) \ cos\ left( \ beta \ right) - \ sin\ left( \ alpha \ right)\ sin\ left(\ beta \ right)

\ cos\ left( \ alpha - \ beta \ right) = \ cos\ left( \ alpha \ right) \ cos\ left( \ beta \ right) + \ sin\ left( \ alpha \ right)\ sin\ left(\ beta \ right)

\ tan\ left( \ alpha + \ beta \ right) = \ frac {  \ tan \ left( \ alpha \ right) + \ tan\ left( \ beta \ right) } {1- \ tan\ left( \ alpha \ right) \ tan \ left( \ beta \ right) }

\ tan\ left( \ alpha -\ beta \ right) = \ frac { \ tan \ left( \ alpha \ right) -\ tan \ left( \ beta \ right) } {1 + \ tan\ left( \ alpha \ right) \ tan \ left( \ beta \ right) }

 \ cot \ left( \ alpha + \ beta \ right) = \ frac { \ cot \ left( \ alpha \ right) \ cot\ left( \ beta \ right) - 1} { \ cot\ left( \ alpha \ right) + \ cot \ left( \ beta \ right)}

 \ cot \ left( \ alpha -\ beta \ right) = \ frac { \ cot \ left( \ alpha \right) \ cot\ left( \ beta \ right) + 1} { \ cot\ left( \ beta \ right) - \ cot \ left( \ alpha \ right)}


PRODUCT TO SUM FORMULAS:


\ sin \ left( \ alpha \ right) \ \ cos \ left( \ beta \ right) = \ frac1\2 \ left[ \ sin \ left( \ alpha + \ beta \ right) + \ sin \ left( \ alpha - \ beta \ right) \ right]

\ cos \ left( \ alpha \ right) \ \ sin \ left( \ beta \ right) = \ frac1\2 \ left[ \ sin \ left( \ alpha + \ beta \ right) - \ sin \ left( \ alpha - \ beta \ right) \ right]

\ cos \ left( \ alpha \ right) \ \ cos \ left( \ beta \ right) = \ frac1\2 \ left[ \ cos \ left( \ alpha + \ beta \ right) + \ cos \ left( \ alpha - \ beta \ right) \ right]

\ sin \ left( \ alpha \ right) \ \ sin \ left( \ beta \ right) = - \ frac1\2 \ left[ \ cos \ left( \ alpha + \ beta \ right) - \ cos \ left( \ alpha - \ beta \ right) \ right]


SUM TO PRODUCT FORMULAS:


 \ sin \ left( \ upsilon \ right) + \ sin \ left( \ nu \ right) = 2 \ sin \ left( \ frac { \ upsilon + \ nu} 2 \ right) \ cos \ left( \ frac { \ upsilon - \ nu} 2 \ right)

 \ sin \ left( \ upsilon \ right) -\ sin \ left( \ nu \ right) = 2 \ cos \ left( \ frac { \ upsilon + \ nu} 2 \ right) \ sin \ left( \ frac { \ upsilon - \ nu} 2 \ right)

 \ cos \ left( \ upsilon \ right) + \ cos \ left( \ nu \ right) = 2 \ cos \ left( \ frac { \ upsilon + \ nu} 2 \ right) \ cos \ left( \ frac { \ upsilon - \ nu} 2 \ right)

 \ cos \ left( \ upsilon \ right) -\ cos \ left( \ nu \ right) = - 2 \ sin \ left( \ frac { \ upsilon + \ nu} 2 \ right) \ sin \ left( \ frac { \ upsilon - \ nu} 2 \ right)


LAW OF SINE:


 \ frac { \ sin \ left( \ alpha \ right) } a = \ frac{ \ sin \ left( \ beta \ right) } b = \ frac{ \ sin \ left( \ gamma \ right) } c

OR

 \ frac a { \ sin \ left( \ alpha \ right) } = \ frac b { \sin \ left( \ beta \ right) } = \ frac c { \ sin \ left( \ gamma \ right) }

OR

 a \ : \ b \ : \ c \  = \  \ sin\ left( \ alpha \ right) \  : \  \ sin \ left( \ beta \ right) \ : \ \ sin \ left( \ gamma \ right)


LAW OF COSINE:


 \ cos \ left( \ alpha \ right) = \ frac { b^2 + c^2 - a^2} { 2bc }

OR

 a^2 = b^2 + c^2 -2bc \ cos \ left( \ alpha \ right)

=====


 \ cos \ left( \ beta \ right) = \ frac { a^2 + c^2 - b^2} { 2ac }

OR

b^2 = a^2 + c^2 -2ac \ cos \ left( \ beta \ right)

=====


 \ cos \ left( \ gamma \ right) = \ frac { a^2 + b^2 - c^2} { 2ab }

OR

c^2 = a^2 + b^2 -2ab \ cos \ left( \ gamma \ right)


HALF ANGLE FORMULAS:


 \ sin \ left( \ frac \alpha2\ right) \ = \ sqrt { \ frac { (s-b) \ (s-c) } { bc } }

 \ sin \ left( \ frac \beta2\ right) \ = \ sqrt { \ frac { (s-a) \ (s-c) } { ac } }

 \ sin \ left( \ frac \gamma2\ right) \ = \ sqrt { \ frac { (s-a) \ (s-b) } { ab } }

 \ cos \ left( \ frac \alpha2\ right) \ = \ sqrt { \ frac { s (s-a) } { bc } }

 \ cos \ left( \ frac \beta2\ right) \ = \ sqrt { \ frac { s (s-b) } { ac } }

 \ cos \ left( \ frac \gamma2\ right) \ = \ sqrt { \ frac { s (s-c) } { ab } }

 \ tan \ left( \ frac \alpha2\ right) \ = \ sqrt { \ frac { (s-b) \ (s-c) } { s (s-a) } }

 \ tan \ left( \ frac \beta2\ right) \ = \ sqrt { \ frac { (s-a) \ (s-c) } { s (s-b) } }

 \ tan \ left( \ frac \gamma2\ right) \ = \ sqrt { \ frac { (s-a) \ (s-b) } { s (s-c) } }


AREA OF A TRIANGLE:


\ triangle = Area


3 SIDES GIVEN:


 \ triangle = \ sqrt { s (s-a) (s-b) (s-c) }

 s = \ frac { a + b + c } 2


2 SIDES INCLUDED ANGLE GIVEN:



 \ triangle = \ frac { bc \ sin \ left( \ alpha \ right) } 2

 \ triangle = \ frac { ac \ sin \ left( \ beta \ right) } 2

 \ triangle = \ frac { ab \ sin \ left( \ gamma \ right) } 2


1 SIDES INCLUDED 2 ANGLES GIVEN:


 \ triangle = \ frac { a^2 \ sin \ left( \ beta \ right) \ sin \ left( \ gamma \ right) } { 2 \ sin \ left( \ alpha \ right) }

 \ triangle = \ frac { b^2 \ sin \ left( \ alpha \ right) \ sin \ left( \ gamma \ right) } { 2 \ sin \ left( \ beta \ right) }

 \ triangle = \ frac { c^2 \ sin \ left( \ alpha \ right) \ sin \ left( \ beta \ right) } { 2 \ sin \ left( \ gamma \ right) }


CIRCUM-RADIUS R IN TERMS OF THE MEASURE OF A THREE SIDES OF A  TRIANGLE:


R \ = \ frac{ \ abc } { 4\triangle}


THE IN-RADIUS OF A TRIANGLE:


r = \ frac \triangle s


RADII OF E-CIRCLES OF A TRIANGLE:


r_1 = \ frac \triangle {s-a}

r_2 = \ frac \triangle {s-b}

r_3 = \ frac \triangle {s-c}