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    I never quite understood how to use the CAST diagram in trig to find several answers to a question, it's always been very hit and miss with me. Since I am retaking C2 and there is a lot of harder trig in C3, I thought it might be time to make sure I know how to use it 100% as I'm not confident at the moment. Could anybody explain, or does anyone have any links to useful videos or websites to help me? Thanks
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    If you look at this diagram:

    Name:  dd4c66c843e1c290f47bf21e6e7bdd39.png
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    'All' means that the values of sinx, tanx, and cosx are all positive in the range 0 - 90.
    In the second quadrant only the values of sinx are positive in the range 90 - 180.
    In the third quadrant, only the values of tanx are positive in the range 180 - 270, and so on.
    Say you find out numerically that, sin- (3/4) is 48.6 degrees.
    You know that your value of sin48.6 is positive, so you need to look in the top two quadrants to find your solutions (i.e, where sinx is positive). Measuring an angle of -48.6 degrees from the negative x axis, you get 180-48.6 = 131.4 degrees, another solution to sin-(3/4).
    For any solutions greater than 360, you relabel the axes. Where it says 0, you'd write 360, going around anticlockwise, 450, 540, 630.
    Your third solution would be 360 + 48.6 = 408.6
    The fourth: 540 - 48.6 =491.4.

    This link I found has really nice clear diagrams for this:

    http://www.statistica.com.au/cast_diagram.html
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    (Original post by louderthanlove)
    I never quite understood how to use the CAST diagram in trig to find several answers to a question, it's always been very hit and miss with me. Since I am retaking C2 and there is a lot of harder trig in C3, I thought it might be time to make sure I know how to use it 100% as I'm not confident at the moment. Could anybody explain, or does anyone have any links to useful videos or websites to help me? Thanks
    I never got it either until I saw this video:



    Hope it helps.
 
 
 
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