Understanding the Cofunction Identities in Trigonometry

[bobsmith76]

Homework Statement

My book is showing 1 - (sin^2)x = (cos^2)x, is this true? If so under what subject do I find more information about this. I found cofunction identities where sin(90° - θ) = cosθ but I'm not sure if that's the same thing.

Homework Equations

The Attempt at a Solution

 

[Curious3141]

Homework Statement

My book is showing 1 - (sin^2)x = (cos^2)x, is this true? If so under what subject do I find more information about this. I found cofunction identities where sin(90° - θ) = cosθ but I'm not sure if that's the same thing.

Homework Equations

The Attempt at a Solution

Just rearrange \sin^2 x + \cos^2 x = 1, which you recently asked about in another thread.

 

[Mentallic]

My book is showing 1 - (sin^2)x = (cos^2)x, is this true?

Yes, draw a right triangle and label one of the angles x. Now label each side a, b and c. Ok so what is sin(x) in terms of a,b,c? So what is sin²(x)? Continue this for cos²(x) and you'll see the result holds.

If so under what subject do I find more information about this.

Basic trigonometry? After being taught about graphing trig functions I believe you're exposed to more trig identities.

 

[bobsmith76]

thanks, i feel stupid, but at least i know the answer

 

[Mentallic]

thanks, i feel stupid, but at least i know the answer

Nah being stupid would be not knowing the answer in the exam