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    Find, in degrees, the value of Theta in the interval of 0<=Theta<360 for which:

    2cos^2Theta – cosTheta – 1 = Sin^2Theta

    I have solved this to get costheta= -2/3 and costheta= 1 but when putting it into my calculator I only get the answer of 131.8 and 0 is this this it?
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    Question, are you in the first or second year?
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    (Original post by Sukjeetsandhu)
    Find, in degrees, the value of Theta in the interval of 0<=Theta<360 for which:

    2cos^2Theta – cosTheta – 1 = Sin^2Theta

    I have solved this to get costheta= -2/3 and costheta= 1 but when putting it into my calculator I only get the answer of 131.8 and 0 is this this it?
    No, there are 2 more solutions. If you sketch the graph of cosx for the given interval you should be able to see the other two solutions.
    Alternatively, you can use the CAST diagram if you have been taught that in class (but this is just a simplification of the graphical approach).

    graph of y = cosx:
    Attachment 609556
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    (Original post by Sukjeetsandhu)
    Find, in degrees, the value of Theta in the interval of 0<=Theta<360 for which:

    2cos^2Theta – cosTheta – 1 = Sin^2Theta

    I have solved this to get costheta= -2/3 and costheta= 1 but when putting it into my calculator I only get the answer of 131.8 and 0 is this this it?

    Find, in degrees, the value of Theta in the interval of 0 \leq \theta &lt;360 for which:

    2cos^2 \theta -cos \theta -1=sin^2 \theta

    Change cos^2 \theta into 1-sin^2 \theta and rearrange to form a quadratic. Then solve for  cos \theta
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    (Original post by Friendly Fatty)
    Question, are you in the first or second year?
    First year
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    Use a mark scheme? lool
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    (Original post by Sukjeetsandhu)
    First year
    Well I am too and have no idea about any of this
 
 
 
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