# Derive Trig Half Angle Identities

Taught by YourMathGal
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Lesson Summary:

In this math lesson, Julie Harland derives the half-angle trig identities for cosine, sine, and tangent. She explains how to use double-angle identities for the cosine of 2x, and then goes on to derive the formulas for the half-angle identities. She shows three formulas for the tangent of a half-angle and explains that if you know the sine and cosine of an angle, you can use these formulas to figure out the sine, cosine, or tangent of half that angle.

Lesson Description:

Video derives the half angle trigonometry identities for cosine, sine and tangent

More free YouTube videos by Julie Harland are organized at http://yourmathgal.com

• What are the trig half angle identities?
• How can you derive the trig half angle identities?
• How can you use the trig double angle identities to derive the half angle identities?
• What is the formula for cos(x/2) and how to you derive it?
• What is the formula for sin(x/2) and how to you derive it?
• What is the formula for tan(x/2) and how to you derive it?
• Why are there multiple formulas for the tan(x/2) and how do you derive them?
• How do you derive the formula tan(x/2) = (sinx)/(1 + cosx)?
• How do you derive the formula tan(x/2) = (1 - cosx)/sinx?
• #### Staff Review

• Currently 4.0/5 Stars.
This lesson is very similar to the previous lesson in this series, but instead of deriving double angle identities, you will learn how to derive the half angle trig identities. Each step in the derivation process is explained.