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Math Help - What exactly is a "Double Angle"?

  1. #1
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    What exactly is a "Double Angle"?

    I had a question about Trig. Double angle formulas….why is it called “double angle”? For instance, say we have Cos 2x. Does this mean we are multiplying the value of the angle by 2 and then taking the Cosine of it? So 150 degrees would 300 degrees? And then we take the Cosine of it? I understand how to calculate these using the formulas, I just don't understand what a double angle is (visually I guess).

    Also, why does Cosine have 3 ways of calculating a double angle and Sine only has 1?
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Slappydappy View Post
    Does this mean we are multiplying the value of the angle by 2 and then taking the Cosine of it?
    That's it exactly.

    -Dan
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Slappydappy View Post
    Also, why does Cosine have 3 ways of calculating a double angle and Sine only has 1?
    It is simply that the form for sin(2x) does not include the square of sine or cosine. We have three different forms for cosine squared becasue we can use the identity sin^2(x) + cos^2(x) = 1 in various ways with it.

    -Dan
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