Trigonometry/Plotting (Cos t, Sin t)
Exercise: Using Sine and Cosine on Your Calculator
It is nowadays very easy to find the value of sin and cos for any angle: many calculators have buttons that give these values, or on a PC you can use the calculator that comes with Windows. Spreadsheets can also calculate these functions.(or cosine) button on your calculator. Type in 60 and press . You should see 0.5 on the screen.
Any number of things could have gone wrong here. You might not have , you might not have a calculator, you might not get the answer 0.5. Here's what to do if it didn't work.
OK. So now type in 60 and this time press (or sine). This time you should get the answer 0.8660... If this is working fine, we'd like you to draw up a table for coordinates. We've filled in some of the values, but you need to fill in the rest.
Whilst you are doing this you might like to check that the values we already filled in are correct. Did we get any wrong? The three rows at the end of the table are for you to choose values of t and then put in cosine and sine values for those values of t. We suggest you chose values for t that are somewhere between -900 and +900.
The piece of graph paper on this page is a clue as to what to do next. We'd like you to treat each of the pairs ( cos t, sin t) as a coordinate of a point on the graph paper and plot those points. Don't join them up yet, just plot the points. All the values you got should be between 1 and -1, so the axes already drawn on the graph should be the right ones. Oh, no one has drawn them yet. For now you will have to do that part too. This book is still being written. Anyway, once you start plotting some of the points you should start to get an idea of what shape is being formed. Even if you know the answer already or can guess it, it can be worth doing this exercise. It gives you a really good sense of what cosine and sine are.
Chances are the shape you have drawn so far is very incomplete. You should be able to choose some values for t that will help to make it more complete.
If you are finding this all ridiculously easy, try and find another values of t that give you the same answer as you got for . You should be able to find at least one.