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Using Sin/Cos/Tan graphs for trigonemetry Watch

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    Hi,

    Currently I have used the CAST quadrant method in C2 to work out angle within limits like:

    cos2x = -0.9

    0 < x < 180

    I know that I should get

    2x = 154.15

    but what do I do after this and how do I use the sin graph to work out the angles?

    Thanks
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    (Original post by Sameer599)
    Hi,

    Currently I have used the CAST quadrant method in C2 to work out angle within limits like:

    cos2x = -0.9

    0 < x < 180

    I know that I should get

    2x = 154.15

    but what do I do after this and how do I use the sin graph to work out the angles?

    Thanks
    You don't; you use the cos graph.

    Pick a value on the y-axis of the cos(2x) graph. Now, go along to see how many times you hit the graph.

    You can effectively read off the solutions using the symmetry of the graph.
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    (Original post by Sameer599)
    Hi,

    Currently I have used the CAST quadrant method in C2 to work out angle within limits like:

    cos2x = -0.9

    0 < x < 180

    I know that I should get

    2x = 154.15

    but what do I do after this and how do I use the sin graph to work out the angles?

    Thanks
    Well, wether you use CAST or the Cos graph you find other values that also have cos(value) = -0.9

    Then you halve your answers to get x


    If using the graph you simply use the symmetry
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    Yep sorry, my mistake.

    Name:  cos-graph.jpg
Views: 88
Size:  9.1 KB

    So this is the cos graph, could you direct it from there please? I also know the limit should be 360 since you times 180 by 2.
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    (Original post by Sameer599)
    Yep sorry, my mistake.

    Name:  cos-graph.jpg
Views: 88
Size:  9.1 KB

    So this is the cos graph, could you direct it from there please? I also know the limit should be 360 since you times 180 by 2.
    Draw a line across at approx -0.9

    use symmetry
 
 
 
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