My Math Forum Confusing trig problem need help

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 October 28th, 2009, 12:23 AM #1 Member   Joined: Oct 2009 Posts: 98 Thanks: 0 Confusing trig problem need help I'm really not sure where to start at all with this one. could be the fact that I've been staring at this homework all day long. Here's the diagram $x^2+y^2=1$ $P(x,y)=P(cos\theta,sin\theta)$ I need to express the area of triangle ABP as a function of $\theta$. I also need to express the slope of line PB as a function of $\theta$ I know the formula to find the area of a circle, so it may be a matter of pluging in some part of the above identities into the formula to find out the answer, I also know the slope formula, but I am just having trouble deciding what to do. I have tried to find a part of the book that would help me with this one, but didn't find anything useful. (which I normally don't when doing homework from this instructor) I know all the trig identities and I have the unit circle memorized. Sometimes the way the problems are worded and put together confuse me, when it is usually something fairly simple. I don't like to ask for help when I haven't tried the problem, however on this one I don't really know where to start. maybe a hint or something. I'm not asking for the answer but maybe some guidance as to how I should approach this one. maybe i'll get some sleep and tackle this one in the morning. Thanks!
 October 28th, 2009, 12:41 AM #2 Member   Joined: Oct 2009 Posts: 39 Thanks: 0 Re: Confusing trig problem need help Area of the triangle is S=1/2 a h where a=AB (always!, your triangle is in the circle) and h=r sin(angledelta) But r=1 so S=1/2 AB sin(angledelta) Slope you can calculate knowing that sum of angles in the triangles gives 180, so angle PBA=(180-angledelta)/2 (as triangle PAB is isosceles, PC=BC, where C is middle of the circle).
 October 28th, 2009, 12:55 AM #3 Member   Joined: Oct 2009 Posts: 98 Thanks: 0 Re: Confusing trig problem need help I'm still a little confused. what is angle delta? could you explain a little better what you mean? Thanks!
October 28th, 2009, 01:20 AM   #4
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Re: Confusing trig problem need help

Quote:
 Originally Posted by suomik1988 I'm still a little confused. what is angle delta? could you explain a little better what you mean? Thanks!

angle delta is just angle you marked with greek character,. I am not sure how to write greek letters here. It is an angle PCB, where C is centre of the circle.

 October 28th, 2009, 02:27 AM #5 Global Moderator   Joined: Dec 2006 Posts: 18,140 Thanks: 1415 In other words, ?. See this article regarding the area of a triangle. For the second problem, you can use the inscribed angle theorem (which gives the equation W300 used).

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# Express the area of Î”ABP as a function of Î¸

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