ANALYTIC TRIGONOMETRY UNIT 7. VERIFYING IDENTITIES LESSON 7.1.
5.2 Verifying Trigonometric Identitiesmrspolandsmath.weebly.com/uploads/3/3/1/0/3310645/trig5... ·...
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5.2Verifying Identities by Working With One Side ▪ Verifying Identities by Working With Both Sides
Verifying Trigonometric Identities
November 30, 2012Mrs. Poland
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Objective #4: Students will be able to verify trigonometric identities.
SC #4: I can verify trigonometric identities by working with one side of an equation.
SC #5: I can verify trigonometric identities by working with both sides of an equation.
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Hints for Verifying Identities
Learn the fundamental identities.
Whenever you see either side of a fundamental identity, the other side should come to mind. Also, be aware of
equivalent forms of the fundamental identities.
Try to rewrite the more complicated side of the equation so that it is identical to the
simpler side.
It is sometimes helpful to express all trigonometric functions in the equation in terms of sine and cosine and then simplify
the result.
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Usually, any factoring or indicated algebraic operations should be performed.
For example, the expression
can be factored as
Hints for Verifying Identities
The sum or difference of two trigonometric expressions such as can be added or subtracted in the same way as any other rational
expression.
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Hints for Verifying Identities
As you select substitutions, keep in mind the side you are not changing, because it represents your goal.
For example, to verify the identity
find an identity that relates tan x to cos x.
Since andthe secant function is the best link between the two sides.
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Hints for Verifying Identities
Similar results for 1 – sin x, 1 + cos x, and 1 – cos x may be useful.
Caution
Verifying identities is not the same a solving equations.
Techniques used in solving equations, such as adding the same terms to both
sides, should not be used when working with identities since you are starting with a statement that may not be true.
If an expression contains 1 + sin x, multiplying both the numerator and denominator by 1 – sin x would give 1 – sin x, which could be replaced
with cos x. 2
2
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Verifying Identities by Working with One Side
To avoid the temptation to use algebraic properties of equations to verify identities, one strategy is to work with only one side and rewrite it to match the other side.
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Example 1 VERIFYING AN IDENTITY (WORKING WITH ONE SIDE)
Verify that is an identity.
Work with the right side since it is more complicated.Right side of given
equation
Distributive property
Left side of given equation
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Example 2 VERIFYING AN IDENTITY (WORKING WITH ONE SIDE)
Verify that is an identity.
Distributive property
Left side
Right side
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Example 3 VERIFYING AN IDENTITY (WORKING WITH ONE SIDE)
Verify that is an identity.
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Example 4 VERIFYING AN IDENTITY (WORKING WITH ONE SIDE)
Verify that is an identity.
Multiply by 1 in the form
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Verifying Identities by Working with Both Sides
If both sides of an identity appear to be equally complex, the identity can be verified by working independently on each side until they are changed into a common third result.
Each step, on each side, must be reversible.
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Example 5 VERIFYING AN IDENTITY (WORKING WITH BOTH SIDES)
Verify that is an identity.Working with the left side:
Multiply by 1 in the form
Distributive property
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Example 5 VERIFYING AN IDENTITY (WORKING WITH BOTH SIDES) (continued)
Working with the right side:
Factor the numerator.
Factor the denominator.
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Example 5 VERIFYING AN IDENTITY (WORKING WITH BOTH SIDES) (continued)
So, the identity is verified.
Right side of given equation
Left side of given equation
Common third expression
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Classwork
Page 194-195 #33-41 odds
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