1. An Introduction to Trig Identities
Section: 4.3
An Introduction to Trig Identities
What is an identity?
Reciprocal Identities

2. Quotient Identities

3. Pythagorean Identities

4. Relationships Between Trig Functions
SIN
COS
SEC
TAN
COT
CSC
Given the value of one trig function, we can use identities to find all the rest!

6. Cofunctions sin 30° = cos 60 ° = 1/2 tan 10° = cot 80°
sec 15 ° = csc 75 °
In general…
Cofunctions of Complements are Equal !
sin  = cos (π/2 – )
The COMPLEMENT of 

7. Know how to evaluate trig functions for special angles
30°
45°
60°
sin
cos
tan

8. Memorize!
30°
45°
60°
sin
cos
tan 1

9. Standing on the ground, a surveyor is 30 ft from the base of a tree
Standing on the ground, a surveyor is 30 ft from the base of a tree. The angle of elevation is 68 degrees.
How tall is the tree?