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 SSAT Upper Level Prep Books (Our 2023 Favorite Picks)
- PERT Math FREE Sample Practice Questions
- Slope Fields Simplified: Understanding the Core of Differential Equations
- Count Lines of Symmetry
- The Ultimate 7th Grade GMAS Math Course (+FREE Worksheets)
- Full-Length 6th Grade Common Core Math Practice Test
- Your Math Buddy: How to Unravel the Mystery of Mutually Exclusive and Overlapping Probabilities
- How is the TExES Core Subjects Scored?
- Top 10 Tips for Managing Time Effectively on the SAT Math
- 10 Most Common 5th Grade Common Core Math Questions
What people say about "Sum and Difference of Trigonometric Functions Formulas - Effortless Math: We Help Students Learn to LOVE Mathematics"?
No one replied yet.