3 Identities
3.1 Basic Trigonometric Identities
So far we know a few relations between the trigonometric functions. For example, we know
the reciprocal relations:
1.
csc
θ
=
1
sin
θ
when sin
θ
n=
0
2.
sec
θ
=
1
cos
θ
when cos
θ
n=
0
3.
cot
θ
=
1
tan
θ
when tan
θ
is de±ned and not 0
4.
sin
θ
=
1
csc
θ
when csc
θ
is de±ned and not 0
5.
cos
θ
=
1
sec
θ
when sec
θ
is de±ned and not 0
6.
tan
θ
=
1
cot
θ
when cot
θ
is de±ned and not 0
Notice that each of these equations is true for
all
angles
θ
for which both sides of the equa
tion are de±ned. Such equations are called
identities
, and in this section we will discuss
several
trigonometric identities
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 Fall '11
 Dr.Cheun
 Calculus, Trigonometry, Trigonometric Identities, Cos, Elementary algebra, basic trigonometric identities

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