# Sum and Difference Formulas in Trigonometry

This is a list of the sum and difference formulas involving the sine,cosine and tangent functions used in trigonometry.

Review

## Sum Formulas

1. sin(x + y) = sin x * cos y + cos x * sin y

2. cos(x + y) = cos x * cos y - sin x * sin y

3. tan(x + y) = [tan x + tan y] / [1 - tan x * tan y]

## Difference Formulas

1. sin(x - y) = sin x * cos y - cos x * sin y

2. cos(x - y) = cos x * cos y + sin x * sin y

3. tan(x - y) = [tan x - tan y] / [1 + tan x * tan y]

More on
• Trigonometric Formulas and Their Applications
and
• Trigonometric Identities and Their Applications