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Thread: Positive angle and negative angle. Explain please.

  1. #1
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    Positive angle and negative angle. Explain please.

    My book says,
    ''consider a ray OA. If this ray revolves about its end point O in an anti-clockwise direction and takes position OB, then we say the angle ∠AOB has been generated as a positive angle and a negative angle. or simply say that angle is a measure or an amount of revolution of a given ray about its initial point.
    The angle is positive or negative if the initial line revolves in anti-clockwise or clockwise direction to get the terminal line''

    Still, I cannot understand the concept. Could you get the point easier for me, please?

  2. #2
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    Quote Originally Posted by Indranil View Post
    My book says,
    ''consider a ray OA. If this ray revolves about its end point O in an anti-clockwise direction and takes position OB, then we say the angle ∠AOB has been generated as a positive angle and a negative angle. or simply say that angle is a measure or an amount of revolution of a given ray about its initial point.
    The angle is positive or negative if the initial line revolves in anti-clockwise or clockwise direction to get the terminal line''

    Still, I cannot understand the concept. Could you get the point easier for me, please?
    The wording is a little odd; did you quote it word for word?

    The basic idea is that anti-clockwise (or counter-clockwise) rotation is considered to be positive, and clockwise rotation is negative.

    I would restate your sentence, "The angle is positive or negative if the initial line revolves in anti-clockwise or clockwise direction to get the terminal line" as "The angle is positive if the initial line revolves in an anti-clockwise direction to the terminal line, and negative if the initial line revolves in a clockwise direction".

    So if we start with OA and rotate 90 degrees clockwise to OB, we say that AOB is -90.

  3. #3
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    1. Could you provide a figure in support of it?
    2. Could you discuss 'initial line' and 'terminal line' so I can understand well, please?

  4. #4
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    Quote Originally Posted by Indranil View Post
    1. Could you provide a figure in support of it?
    2. Could you discuss 'initial line' and 'terminal line' so I can understand well, please?
    Does your book not have a picture? That is difficult to believe.

    What part do you not understand? Are you saying you don't know what "initial" and "terminal" mean? Please be specific; I can't help you understand without knowing where you need help.

    Let's look for a picture and explanation online. Here are two I found by searching for "signed angles initial terminal": Oxford Math Center; Math Open Reference. There are many more.

    Where you used the word "line", these use "side".

  5. #5
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    I understand now. Thank you for your kind effort. Thanks a lot.

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