2. Definition
A trigonometric identity is a
statement of equality
between two expressions.
It means one expression
can be used in place of the
other.
A list of the basic identities
can be found on p.460 of
your text.
19. Try This
Use the
Pythagorean
Identities to find
sin t for the given
value of cos t.
Make sure the
sign is correct for
the given
quadrant.
2
cos
5
t =
3
2
2
t
π
π< <
5
5
−
21. Important Idea
To solve trigonometric
identity problems, you
may use more than one
identity in the same
problem.
22. Try This
If , find
2
cos
3
θ = tanθ
Assume θ is between 0 & 2
π
5
tan
2
θ =
23. Example
If and t is in
quadrant I, find the 5
remaining trig functions.
cos .3586t =
24. Try This
If
and t is in
quadrant II,
find the 5
remaining trig
functions.
sin .2985t = cos .9544t = −
tan .3128t = −
sec 1.0478t = −
csc 3.3501t =
cot 3.1969t = −