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    hey
    I am wondering if anyone could help me on this maths question

    solve this equation 4 sec 2x = -7

    between 0°≤x≤360°

    thanks
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    Turn sec into cos and try rearranging the equation into a form cos(2x) = something.
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    i got to cos 2x = -1/7 - don't know if this is right

    what shall i do next?
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    (Original post by Lehmber Hussainpuri)
    i got to cos 2x = -1/7 - don't know if this is right

    what shall i do next?
    4sec2x = -7
    4/cos2x = -7
    4 = -7cos2x
    cos2x = -4/7

    Do you know how to solve that? If not, think about how you'd solve this:

    cos y = -4/7

    If you know cos y = -4/7, how can you work out cos 2x = -4/7? Can you see a similarity about cos y and cos 2x in this case? They're equal. So y = 2x.
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    thanks i get it now
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    Also don't forget that the range of 2x is:

    0≤2x≤720

    So when solving:

    cos 2x = -4/7

    You need the solutions from 0 to 720 so that when you halve them (to get values for x) they will be between 0 and 360
 
 
 
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