Graphing Trigonometry Equations

Date: 5/15/96 at 15:4:32
From: Anonymous
Subject: Graphing Trigonometry Equations

I am currently taking Mathematics 12 through correspondance, and I 
haven't had very much trouble so far. But recently I came upon a 
subject which the textbook barely covers. Here is an example that is 
meant to be graphed:

        Cos A Cos 3A - Sin A Sin 3A

This is equal to Cos (A + 3A) or Cos 4A.

But how do I graph this one:

        Sin A - Cos A

Is there an identity that I am forgetting?  Thanks for your help.

Aaron S.

Date: 11/11/96 at 22:46:53
From: Doctor Robert
Subject: Re: Graphing Trigonometry Equations

I am not sure that I completely understand your question.  If you are 
to graph y = sin x - cos x, you can make a table of values and plot 
the graph without resorting to any identity to simplify it.  This 
function can be very easily graphed on a graphing calculator.  If you 
need to have the function in terms of only one trig function, you 
could use the fact that 

   cos A = sqrt(1 - sin^2 A)
 
so that your function would be:

   y = sin A - sqrt(1 - sin^2 A) 

if that makes it any easier!

-Doctor Robert,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/