Double Angle Identities

Examples, solutions, videos, worksheets, games and activities to help PreCalculus students learn about the double angle identities.

The following diagram gives the Double-Angle Identities. Scroll down the page for more examples and solutions.

 

What are the Double-Angle Identities or Double-Angle Formulas?
sin(2x) = 2sin(x)cos(x)
cos(2x) = cos²(x) - sin²(x) = 1 - 2sin²(x) = 2cos²(x) - 1

How to use the Double-Angle Identities or Double-Angle Formulas?
Double-Angle Formulas
A few examples that use double-angle formulas from trigonometry.

Using Double Angle Identities to Solve Equations

How to proof the Double-Angle Identities or Double-Angle Formulas?
Double Angle Formulas :
The double angles sin(2x) and cos(2x) can be rewritten as sin(x + x) and cos(x + x).
Applying the cosine and sine addition formulas, we find that sin(2x) = 2sin(x)cos(x).
Also, cos(2x) = cos²(x) - sin²(x)
How to use the sine and cosine addition formulas to prove the double-angle formulas.

Check out our most popular games!
Fraction Concoction	Fact Family Game	Number Bond Garden
Online Addition Subtraction Game	Penguin Solitaire	Sawayama Solitaire
Ark Solitaire	Eldritch Invasion	Shenzhen Solitaire

Check out more Solitaire games here.

We welcome your feedback, comments and questions about this site or page. Please submit your feedback or enquiries via our Feedback page.