# Product To Sum Identities and Sum To Product Formulas - Trigonometry | Summary and Q&A

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October 20, 2017
by
The Organic Chemistry Tutor
Product To Sum Identities and Sum To Product Formulas - Trigonometry

## TL;DR

Learn how to apply trigonometric product-to-sum formulas to simplify trigonometric expressions and verify identities.

## Key Insights

• 🍹 Four trigonometric product-to-sum formulas are introduced: sin(alpha)cos(beta), cos(alpha)cos(beta), sin(alpha)sin(beta), and cos(alpha)sin(beta).
• 😑 The video demonstrates how to simplify trigonometric expressions using the product-to-sum formulas, providing step-by-step examples.
• 🍹 Four sum-to-product formulas are explained: sine(alpha) + sine(beta), sine(alpha) - sine(beta), cosine(alpha) + cosine(beta), and cosine(alpha) - cosine(beta).
• 😑 The content showcases examples of simplifying expressions using the sum-to-product formulas.
• 😑 One example illustrates how to prove an identity by simplifying an expression to a known trigonometric function.

## Transcript

now let's review the product to some formulas here's the first one sine alpha cosine beta is equal to one-half times cosine alpha minus beta minus cosine alpha plus beta so that's the first one you need to know now let's write the other three the next one is cosine alpha times cosine beta and that's equal to one-half cosine alpha minus beta and thi... Read More

### Q: What are the four trigonometric product-to-sum formulas mentioned in the content?

The four formulas are: sin(alpha)cos(beta), cos(alpha)cos(beta), sin(alpha)sin(beta), and cos(alpha)sin(beta).

### Q: How can we use the product-to-sum formulas to simplify trigonometric expressions?

By substituting the values of alpha and beta from the expression into the corresponding product-to-sum formula, we can simplify the expression to a more manageable form.

### Q: What are the four sum-to-product formulas discussed in the content?

The four sum-to-product formulas are: sine(alpha) + sine(beta), sine(alpha) - sine(beta), cosine(alpha) + cosine(beta), and cosine(alpha) - cosine(beta).

### Q: What is the purpose of the sum-to-product formulas?

The sum-to-product formulas allow us to simplify expressions with the sum or difference of trigonometric functions by converting them into products.

## Summary & Key Takeaways

• The content introduces four trigonometric product-to-sum formulas: sin(alpha)cos(beta), cos(alpha)cos(beta), sin(alpha)sin(beta), and cos(alpha)sin(beta).

• The video demonstrates how to use these formulas to simplify trigonometric expressions, providing examples such as sin(7x)sin(4x) and sin(9x)cos(3x).

• Additionally, the content covers four sum-to-product formulas: sine(alpha) + sine(beta), sine(alpha) - sine(beta), cosine(alpha) + cosine(beta), and cosine(alpha) - cosine(beta).

• The video provides examples of simplifying expressions using the sum-to-product formulas, including sine(8x) + sine(3x) and cosine(11x) + cosine(3x).

• Lastly, the content showcases an example of proving an identity by simplifying sin(x) + sin(3x) / cos(x) + cos(3x) to tangent(2x).