More Lessons for PreCalculus
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?
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
How to use the sine and cosine addition formulas to prove the double-angle formulas.
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