Khan Academy
Khan Academy: Trigonometry: Trig Identities Part 2
Video deriving the double angle formulas for sine and cosine as well as the start of finding the cosine of the opposite of an angle. Reviews basic trigonometric ratio definitions and some basic trigonometric identities. [9:57]
Khan Academy
Khan Academy: Trigonometry: Trigonometry Identity Review/fun
Video showing how to derive additional trigonometric identities, including the double angle formulas, from the sine and cosine of the sum and difference of two angles. Includes link to additional practice problems. [11:07]
Khan Academy
Khan Academy: Trigonometry: Iit Jee Trigonometric Constraints
Video shows solving a trigonometry problem to find the number of values in a given range that satisfy certain conditions. Trigonometric identities are used. [12:49]
Khan Academy
Khan Academy: Trigonometry: Iit Jee Trigonometry Problem 1
Video demonstrates simplifying a trigonometric expression relating unknown sides and angles of a triangle by using trigonometric identities. [15:13]
Khan Academy
Khan Academy: Trigonometry: Iit Jee Trigonometric Maximum
Video demonstrates finding the maximum of a trigonometric expression that is simplified by using trigonometric identities. [9:54]
Khan Academy
Khan Academy: Trigonometry: 2003 Aime Ii Problem 14
Video demonstrates solving a trigonometric problem that includes finding the area of a convex equilateral hexagon in the coordinate plane using trigonometric identities and the Pythagorean Theorem. [18:18]
Khan Academy
Khan Academy: Trigonometry: Proof: Law of Sines
Video deriving the law of sines. Includes discussion of why it is useful. [6:33]
Khan Academy
Khan Academy: Trig Identities: Trigonometric Identities
Video showing how to derive two basic trigonometric identities.
Khan Academy
Khan Academy: Trig Identities: Proof: Cos(a+b) = (Cos A)(cos B) (Sin A)(sin B)
Video demonstrating the proof for the formula for the cosine of the sum of two angles.
Khan Academy
Khan Academy: Trig Identities: Proof: Sin(a+b) = (Cos A)(sin B) + (Sin A)(cos B)
Video demonstrating the proof for the formula for the sine of the sum of two angles.
Study Pug
Study Pug: Quotient Identities and Reciprocal Identities
Don't be scared by all the trigonometric identities formulas! This video will show you how to easily simplify and prove quotient identities and reciprocal identities. [7:27]