# trig

```c 2012 Math Medics LLC. All rights reserved.
TRIGONOMETRIC IDENTITIES
• Reciprocal identities
1
1
sin u =
cos u =
csc u
sec u
1
1
tan u =
cot u =
cot u
tan u
1
1
csc u =
sec u =
sin u
cos u
• Pythagorean Identities
• Power-Reducing/Half Angle Formulas
1 − cos(2u)
2
1 + cos(2u)
cos2 u =
2
1 − cos(2u)
tan2 u =
1 + cos(2u)
sin2 u =
sin2 u + cos2 u = 1
1 + tan2 u = sec2 u
1 + cot2 u = csc2 u
• Quotient Identities
sin u
cos u
tan u =
cot u =
cos u
sin u
• Co-Function Identities
π
π
sin( − u) = cos u cos( − u) = sin u
2
2
tan(
csc(
π
π
− u) = cot u cot( − u) = tan u
2
2
π
− u) = sec u
2
sec(
π
− u) = csc u
2
• Parity Identities (Even &amp; Odd)
sin(−u) = − sin u cos(−u) = cos u
tan(−u) = − tan u cot(−u) = − cot u
csc(−u) = − csc u sec(−u) = sec u
• Sum &amp; Difference Formulas
sin(u &plusmn; v) = sin u cos v &plusmn; cos u sin v
cos(u &plusmn; v) = cos u cos v ∓ sin u sin v
tan u &plusmn; tan v
tan(u &plusmn; v) =
1 ∓ tan u tan v
• Double Angle Formulas
sin(2u) = 2 sin u cos u
cos(2u) = cos2 u − sin2 u
= 2 cos2 u − 1
= 1 − 2 sin2 u
2 tan u
tan(2u) =
1 − tan2 u
• Sum-to-Product Formulas
u−v
u+v
cos
sin u + sin v = 2 sin
2
2
sin u − sin v = 2 cos
u+v
2
cos u + cos v = 2 cos
u+v
2
cos u − cos v = −2 sin
sin
u+v
2
u−v
2
cos
u−v
2
sin
u−v
2
• Product-to-Sum Formulas
sin u sin v =
1
[cos(u − v) − cos(u + v)]
2
cos u cos v =
1
[cos(u − v) + cos(u + v)]
2
sin u cos v =
1
[sin(u + v) + sin(u − v)]
2
cos u sin v =
1
[sin(u + v) − sin(u − v)]
2
```