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Ch. 1 - Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 1, Problem 1.3.36

Using the Addition Formulas


Use the addition formulas to derive the identities in Exercises 31–36.


sin (A − B) = sin A cos B − cos A sin B

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1
Start by recalling the addition formula for sine, which is: sin(A+B)=sinAcosB+cosAsinB.
To derive the formula for sin(A-B), use the identity for sine of a negative angle: sin(-x)=-sinx.
Apply the identity to the addition formula: sin(A-B)=sin(A+-B).
Substitute -B into the addition formula: sinAcos(-B)+cosAsin(-B).
Use the identities cos(-x)=cosx and sin(-x)=-sinx to simplify: sinAcosB-cosAsinB.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Addition Formulas

Addition formulas are trigonometric identities that express the sine and cosine of the sum or difference of two angles in terms of the sines and cosines of the individual angles. For example, the sine of the difference of two angles, sin(A - B), can be expressed as sin A cos B - cos A sin B. These formulas are essential for simplifying expressions and solving trigonometric equations.
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Trigonometric Identities

Trigonometric identities are equations that hold true for all values of the variables involved, provided they are within the domain of the functions. They are fundamental in calculus and trigonometry for transforming and simplifying expressions. The addition formulas are a subset of these identities, allowing for the manipulation of sine and cosine functions in various mathematical contexts.
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Derivation Techniques

Derivation techniques involve the methods used to prove or derive mathematical identities from established formulas. In the context of trigonometric identities, this often includes algebraic manipulation, substitution, and the application of known identities. Understanding these techniques is crucial for effectively deriving new identities, such as the sine and cosine addition formulas.
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Derivatives