Sum and Difference of Trigonometric Functions Formulas
The sum and difference formulas help us evaluate the value of trigonometric functions at angles that can be expressed as the sum or difference of specific angles. In this guide, you will learn more about the sum and difference formulas.

The formulas for sum and difference in trigonometry are used to find the value of trigonometric functions at specific angles where it is easier to express the angle as a sum or the difference of unique angles \(0^{\circ },\:30^{\circ },\:45^{\circ },\:60^{\circ },\:90^{\circ },\:180^{\circ }\).
Related Topics
A step-by-step guide to sum and difference formulas
We have six sum and difference formulas for the trigonometric functions including the sine function, cosine function, and tangent function.
These formulas help us to estimate the value of trigonometric functions at angles that can be expressed as the sum or difference of specific angles \(0^{\circ },\:30^{\circ },\:45^{\circ },\:60^{\circ },\:90^{\circ },\:180^{\circ }\)
The list of sum and difference formulas is as follows:
- \(\color{blue}{sin\:\left(A\:+\:B\right)=\:sin\:A\:cos\:B\:+\:cos\:A\:sin\:B}\)
- \(\color{blue}{sin\:\left(A\:-\:B\right)=\:sin\:A\:cos\:B\:-\:cos\:A\:sin\:B}\)
- \(\color{blue}{cos\:\left(A\:+\:B\right)=\:cos\:A\:cos\:B\:-\:sin\:A\:sin\:B}\)
- \(\color{blue}{cos\:\left(A\:-\:B\right)\:=\:cos\:A\:cos\:B\:+\:sin\:A\:sin\:B}\)
- \(\color{blue}{tan\:\left(A\:+\:B\right)=\:\frac{\:\left(tan\:A+\:tan\:B\right)}{\:\left(1-\:tan\:A\:tan\:B\right)}}\)
- \(\color{blue}{tan\:\left(A\:-\:B\right)=\:\frac{\:\left(tan\:A\:-\:tan\:B\right)}{\:\left(1+\:tan\:A\:tan\:B\right)}}\)
Sum and Difference Formulas – Example 1:
Find the value of \(cos 105°\).
Solution:
We can write \(105°\) as \(105°= 60° + 45°\). So, using the sum formula of \(cos\), \(\color{blue}{cos\:\left(A\:+\:B\right)=\:cos\:A\:cos\:B\:-\:sin\:A\:sin\:B}\)
\(cos 105° = cos\:\left(60°\:+\:45°\right)= cos\:60°\:cos\:45°\:-\:sin\:60°\:sin\:45°\)
\(= (\frac{1}{2}) (\frac{\sqrt{2}}{2}) – (\frac{\sqrt{3}}{2})(\frac{\sqrt{2}}{2})\)
\(=\frac{1}{2\sqrt{2}} – \frac{\sqrt{3}}{2\sqrt{2}}\)
\(=\frac{1-\sqrt{3}}{2\sqrt{2}}\)
Exercises for Sum and Difference Formulas
Find the value of each trigonometric function.
- \(\color{blue}{cos\:\frac{5\pi }{12}}\)
- \(\color{blue}{tan\:15^{\circ }}\)
- \(\color{blue}{sin\:75^{\circ }}\)

- \(\color{blue}{ \frac{\sqrt{6}-\sqrt{2}}{4}}\)
- \(\color{blue}{2-\sqrt{3}}\)
- \(\color{blue}{\frac{\sqrt{2+\sqrt{3}}}{2}}\)
Related to This Article
More math articles
- Top 10 CBEST Prep Books (Our 2023 Favorite Picks)
- 5th Grade SBAC Math FREE Sample Practice Questions
- Full-Length DAT Quantitative Reasoning Practice Test
- Algebra Puzzle – Challenge 35
- The Ultimate ACCUPLACER Math Formula Cheat Sheet
- The Role of Statistics in Analyzing Sports Performance
- 10 Most Common 3rd Grade IAR Math Questions
- Top 10 Free Websites for SAT Math Preparation
- 6th Grade ACT Aspire Math FREE Sample Practice Questions
- How to Graph Solutions to One-step and Two-step Linear Inequalities
What people say about "Sum and Difference of Trigonometric Functions Formulas - Effortless Math: We Help Students Learn to LOVE Mathematics"?
No one replied yet.