Let and

First, we can rewrite using the identity

Its good to note that and [why do you think this is the case?]. So our expression can be written as

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Now let's construct two different triangles, one that has an angle and an angle

Starting with , we see that the side opposite of the angle has a value of and that the hypotenuse has a value of . Using the pythagorean theorem, we can find the value of the adjacent side:

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Now, we construct at triangle for . We see that the side adjacent of the angle has a value of and that the hypotenuse has a value of . Using the pythagorean theorem, we can find the value of the opposite side:

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Now what do you think equals?

--Chris