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    • Thread Starter

    Could someone please help on this question:

    i) Draw the graph of half cos theta, within the interval -360 >theta>360 , marking clearly the points where the values are.


    Do I just do a normal cos graph but then find the values in the interval using a calculator and just mark them down ? I haven't done a question thats asked to draw them before so I'm not really sure.

    You're trying to draw y=\frac{1}{2}cos\theta so draw the graph of y=cos\theta then stretch it by a scale factor of 1/2 parallel to the y-axis. The max points are at y = 0.5, min points at y = -0.5 .

    I take it your finding intersections with y = 0 (theta axis)? If so, then set cos\theta = 0\Rightarrow \theta=cos^{-1}0. That gets you the first value. From the graph you should be able to get the other values. However, I like to use a cast diagram (in my head) and I know that to get the second value of theta, you do 360-\theta. You now have your two main values. Then just add or subtract multiples of 360 from both values to get all possible values in the range. Check it against the number of intersections on the graph to ensure you worked out all of the values of theta .

    I take it that by values you mean the crossing points. Draw the graph, then mark on the graph any point where the curve crosses the axes, it doesn't matter whether you work these out on the calculator, or from knowing the values where cos(theta) crosses the axes.

    1/2cos(theta) is a simple transformation (times Y values by 1/2). This means the graph will be slightly different to the normal cos graph.

    EDIT: Beaten to it , the guy above explained it better ^^
    • Thread Starter

    Thanks for the help both =)
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