Sine and Cosine Stating Negative Numbers the Radians 2

Now look at this wikipedia pics again that I plagiarized.

I am too lazy to draw my own work and lazy is good.

our cosine function has a little change of definition. Rather than the ratio between the length of the near side to the tilted side, now it’s how far to the right the near side is.

Now from the pics, it’s obvious that

cos(θ)=cos(-θ)

or I can more conveniently type

cos(x)=cos(-x)

Reversing that angle do not change the cosine.

It’s not true for the sine. When the angle goes negative, then the side with the front angle start pointing downward. Hence we have

sin(x)=-sin(x).

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• December 13, 2010 -- Sine and Cosine Stating Negative Numbers the Radians 1