Double Angle Identities & Formulas of Sin, Cos & Tan - Trigonometry

This trigonometry video tutorial provides a basic introduction to the double angle identities of sine, cosine, and tangent. It explains how to derive the double angle formulas from the sum and difference identities of sin, cos, and tan and how to use the double angle formulas to find the exact value of trigonometric expressions using right triangle trigonometry and SOHCAHTOA. This video contains many examples and practice problems for you to learn this material.

Bearing Problems and Navigation:

Two Triangle Problems - More Examples:

Verifying Trigonometric Identities:

Sum and Difference Identities:

Verifying Trig Identities With Double Angles:

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Power Reducing Formulas:

Half Angle Formulas:

Verifying Trig Identities Using Half Angles:

Inverse Trig Functions With Double Angles:

Right Triangle Trig With Half Angle Identities:

Product To Sum + Sum to Product Formulas:

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Solving Trig Equations - Finding All Solutions:

Solving Trig Equations With Multiple Angles:

Solving Trig Equations With Double Angles:

Trigonometry Final Exam Review:

Final Exams and Video Playlists:

Full-Length Videos and Worksheets:

Trigonometry Formula Sheet:

[jorgeleiva]

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[jn]

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[georgesadler]

MR. Organic Chemistry Tutor, thank you for a fantastic video on Double Angles Identities and Formulas of Sine, Cosine and Tangent.

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[alster]

For cos 2x there are 3 possible formulae


1.) cos 2x = cos²x-sin²x
The next two are obtained from Pythagorean Identities

First cos²x = 1-sin²x

cos 2x= 1-sin²x-sin²x

2.) cos 2x = 1-2sin²x

And also sin²x= 1-cos²x

Reverting to the first formula and substitution we get

cos 2x = cos²x-(1-cos²x)

We finally have

3.) cos 2x = 2cos²x-1

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[Agoobernamedseth]

This really helped me with double angles, thank you so much 🙏

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[CKDesigner]

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