Pre-Calculus: Fundamental Trigonometric Identities

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In this lesson, Professor Burger will reveal and explain several basic trigonometric identity proofs. He will begin by reviewing the definitions of sine, cosine, and tangent. From these definititions, he will prove tanx = sinx/cosx. Then, he uses the Pythagorean Theorem to show you the proofs for 3 more trigonometric identities: cos^2 + sin^2 = 1, 1+ tan^2 = sec^2, and 1 + cot^2 = csc^2. Finally, Professor Burger will tell you which of these identities and proofs you need to memorize and which you can derive simply and don't need to fret about memorizing in advance of your test.

Taught by Professor Edward Burger, this lesson was selected from a broader, comprehensive course, Precalculus.

Category:

Education

Tags:

• trig
• identities
• trigonometry
• trigonometric
• prove
• proof
• tan
• sin
• cos

[MikeDunn]

You don't have to memorize this. Just remember Soh - Cah - Toa.

[deathbyboredom91]

better yet, why purple and orange?

[iSuperSmashBros]

can anyone help me with this: tan(2x) – sin(2x) = 2tan(2x)sin^2(x) ? Thanks :) Any help would be greatly appreciated!

[EdwardCullensMayo]

@deathbyboredom91 clemson colors :)

[sohoyankee66]

@elmersglue16 Now that I'll remember! Thanks for posting....

[MikeDunn]

@b112895 same thing, dude.  And you spelled hippie incorrectly.

[b112895]

@MikeDunn WRONG its

Some Other Hyppie

Caught Another Hyppie

Tripping On Acid

[Solcito1235]

I love this guy so much

[BorealNeal]

awwww i was learning about trig identities come on

[DoubleAIV]

lol 5 idoit STILL failed their quiz

[chelitogohan]

just remember the SOH (Opposite over Hypotenuse) CAH(Adjacent over Hypotenuse) and TOA(Opposite over Adjacent)

[elmersglue16]

Or Some Old Hippie Caught A High Trippin On Acid