Basic Trigonometric Identities: Pythagorean Identities and Cofunction Identities

Now that we know what these trigonometric functions are, how do they relate to one another? In a variety of ways, in fact! There are lots of identities we will have to learn so that we can do algebra with trig functions later, so let's learn these now.

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[ryanjamesfuentesconiendo]

thanks prof dave.. you saved my 1 semester of math analysis
More power & GOD BLESS YOU MORE

[shygirl]

Just exactly what I was looking for. Thanks you’re the nicest Dave I know

[uchechukwuntinuokwu]

Thank you sir. You just made my understanding of trigonometric identities a lot better.

[falia]

Thanks so much for this video! i really appreciate the part where you derive the other pythagorean identities from that one identity. Our prof never really discussed the connection between the trigo identities so it was quite difficult to comprehend the need for these stuff to me but then I came across this vid so they made so MUCH sense now and it really helped me alot :))

[CJCREATIONS]

Please do, they're great, this is my first time watching you(apart from brady's videos), and out of all the videos I watched(because I had difficulty accepting it) yours was THE BEST, even better than MITOCW.

[Aristos_Arete]

I appreciate your content, I love to learn so this is a treat for me.

[sarafeliciano]

Hi Dave! Decided to go back to university after 10 years...not studying math lol thanks for the super easy refresh! best!

[studyaccount]

came here because i misclicked from graphing functions, stayed for the pythagorean identity derivations. if this was how it was taught to me in 8th grade, i would've liked maths a bit.

[crazyjester]

3:48 sin 30 = cos 90 -30 (because of unit circle theorem)

[shahzaibali]

hi sir i want to clear my problems about cofunctions can you explain with example

[deepanitin]

sir how do u obtain cofunction identitis for 270+x etc..

[littleretroship]

If (sin θ)²+(cos θ)²=1, then does sqrt((sin θ)²+(cos θ)²)=(sin θ)²+(cos θ)² because sqrt(1)=1?

[joschaberg]

Addressing Cofunction Identities:
Why do we define them as e.g.
sin(θ) = cos(90° - θ)
when we could also write:
sin(θ) = cos(θ ± 90°)
?

I assume direction to which we shift the angle does not matter als long as we shift for exactly 90°.

[Alex-]

I never understood why in the US they always teach students secant, cosecant and cotangent. I feel like they are never really that useful for more advanced topics and just add more confusion for students just learning about them.

[nonorv]

Oh no. Why the answers are not explained? 😭 sad!!!

[sristisingh]

arr sir ji Indian bn ke padhao yaar.... hmlog Indian h... okk