
Concept explainers
To write:
Each of all the other trigonometric functions of θ in terms of cosθ.

Answer to Problem 1PS
Solution:
All the other trigonometric functions of θ in terms of cosθ are:
sinθ=±√1−cos2θ,tanθ=±√1−cos2θcosθ,cscθ=1±√1−cos2θ,cotθ=cosθ±√1−cos2θ, and
secθ=1cosθ.
Explanation of Solution
Formula:
Reciprocal identities:
sinu=1cscu,cosu=1secu,tanu=1cotucscu=1sinu,secu=1cosu,cotu=1tanu,
Quotient Identities:
tanu=sinucosu,cotu=cosusinu
Pythagorean Identities:
sin2u+cos2u=11+tan2u=sec2u1+cot2u=csc2u
Calculation:
Consider the provided trigonometric function cosθ. All the other trigonometric functions has to be expressed in terms of cosθ.
Use the Pythagorean identity sin2u+cos2u=1 to calculate sinθ. So,
sin2θ+cos2θ=1
Subtract cos2θ from each side of the equation.
sin2θ+cos2θ−cos2θ=1−cos2θsin2θ=1−cos2θ
Take square root on both the sides of the equation.
√sin2θ=√1−cos2θsinθ=±√1−cos2θ
Now, use the reciprocal identity cscu=1sinu and substitute sinθ=±√1−cos2θ to calculate cscθ.
cscθ=1sinθ=1±√1−cos2θ
By the reciprocal identity secu=1cosu, secθ is calculated in terms of cosθ as,
secθ=1cosθ
Use the quotient identity tanu=sinucosu and substitute sinθ=±√1−cos2θ to calculate tanθ. So,
tanθ=±√1−cos2θcosθ
By the reciprocal identity cotu=1tanu, cotθ is calculated in terms of cosθ as,
cotθ=1tanθ=1±√1−cos2θcosθ=±cosθ√1−cos2θ
Thus, all the other trigonometric functions are expressed in terms of cosθ.
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Chapter 5 Solutions
Bundle: Precalculus, Loose-leaf Version, 10th + WebAssign Printed Access Card for Larson's Precalculus, 10th Edition, Single-Term
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