Chapter 7

```5-Minute Check Lesson 7-1A
Chapter 7
Trigonometric Identities and Equations
Section 7.1
Basic Trigonometric Identities
Definitions
Identity – A statement of equality between two expressions that is true for all values
of the variable(s) for which the expressions are defined.
ex:  2 −  2 =  −   +
Trigonometric Identity – is an identity involving trigonometric expressions.
ex:
sin
cos
= tan
=

=

=

=

=

=

Opposite Angle Identities
(−) = −
− =
Definitions continued
Quotient Identities –

=

Pythagorean Identities –
Recall with the unit circle we knew :  2 +  2 = 1
And we know : cos  = , sin  =
By substitution :  2  + 2  = 1
Which we write as:
+   =
If we divide both sides by sine…
+   =
If we divide both sides by cosine…
+  =
=
Examples
Use the given information to find the trigonometric values
3
2
1. If sec  = , find cos .
4
3
2. If csc  = , find tan  when cos  > 0
1
5
3. If sin  = − , find cos  when tan  < 0
Prove that each equation is not a trigonometric identify by producing a counterexample
1. sin  cos  = cot
2.
sec
tan
= sin
3. sin  + cos  = 1
More Examples:
Simplify:
sin  + sin   2
1. Look for any GCFs: *  ∗
sin  (1 +  2 )
2. Look for any identities: * 1 +  2  ∗
sin  ( 2 )
sin  (
3. Change everything to sines and cosines
4. Simplify
5. Simplify
1
sin
1
)
2
csc
Simplify: cos  tan  + sin  cot
Simplify: 1 +  2  −  2  −  2  2
THESE STEPS ARE NOT IN ANY ORDER. EACH PROBLEM IS SPECIAL
AND YOU MUST OPEN YOUR MIND TO HOW TO SOLVE THEM. Your
answers will always be 1 term, 1 number or a binomial left with sine and
cosine only 
Homework:
Page 427: #19 – 51 Odd, 57, 69
You Try It
You try It
Section 7.2
Verify Trigonometric Identities
Suggestions for Verifying trigonometric Identities
1.
2.
3.
4.
5.
Transform the more complicated side of the equation into the simplier side.
Substitute one or more basic trigonometric identity to simplify expression.
Factor or multiply to simplify
Multiply expressions by an expression equal to 1.
Express all trigonometric functions in terms of sine and cosine.
Example: Verify that  2  − tan  cot  = 2
1
2
− tan
= 2
tan
2  − 1 = 2
2  + 1 − 1 = 2
2  = 2
Lesson Overview 7-2A
Lesson Overview 7-2B
Lesson Overview 7-2C
You Try It
You Try It
Section 7.3
Sum and Difference Identities
Sum and Difference Identities
Sum/Difference Identity for Sine
sin( ± ) = sin  cos  ± sin  cos
*SINE = SIGN SAME*
Sum/Difference Identity for Cosine
cos( ± ) = cos  cos  ∓ sin  sin
*COSINE = NO SIGN SAME*
Sum/Difference Identity of Tangent
tan  ± tan
tan( ± ) =
1 ∓ tan  tan
*TANGENT – SAME/DIFFERENT*
Lesson Overview 7-3A
Lesson Overview 7-3B
Lesson Overview 7-3C
Examples
1. cos 105°
2. sin 165°

3. sin 12
4. tan
23
12
5. sec 1275°

6. Find the exact value if 0 <  < and 0 <  <
2
3
24
cos( − )  cos  =  cos  =
5
25

2
Homework:
Page 442: #15-31 Odd, 34-38 All, 40,42
5-Minute Check Lesson 7-4A
5-Minute Check Lesson 7-4B
Lesson Overview 7-4A
Lesson Overview 7-4B
5-Minute Check Lesson 7-5A
5-Minute Check Lesson 7-5B
Lesson Overview 7-5A
5-Minute Check Lesson 7-6A
Lesson Overview 7-6A
Lesson Overview 7-6B
5-Minute Check Lesson 7-7A
5-Minute Check Lesson 7-7B
Lesson Overview 7-7A
Lesson Overview 7-7B
```