6.3.3 cofunctions, other identities. in some situations, you may know information pertaining to one...
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6.3.3 Cofunctions, Other Identities
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• In some situations, you may know information pertaining to one trig identity/function, but not another– Ex. You know the cos of some angle ϴ, but not ϴ
itself– How would you find sin(ϴ)?
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• Luckily, some trig functions are related to each other, thanks to the unit circle
• Cofunction Identities = equations to use for reference/simplifying particular expressions
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Cofunctions
• If you know the angle ϴ in radians, then:
• cos(ϴ) = sin(π/2 - ϴ)
• csc(ϴ) = sec(π/2 - ϴ)
• cot(ϴ) = tan(π/2 - ϴ)
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• Example. Express cos(5π/11) in terms of its cofunction.
• Example. Express cot(2100) in terms of its cofunction.
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• Example. What is an equivalent trig identity to cos(870)?
• Example. What is an equivalent trig identity to sin(π/6)?
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• Example. Given cot(ϴ) = 0.4, and ϴ lies in the fourth quadrant, determine sin(ϴ).– Hint. What ratio gives us cot(ϴ)?
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• Assignment• Pg.498• 64-67 all• 69-77 odd