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midyearnc

Joined: Jun 5, 2006
Posts: 16
Status: Offline

 PRECAL HELP!!! Reply to this Post Reply with Quote

This question has me stumped. If anyone can help me solve it I would appreciate it.

The rectangular coordinates of a point are (1, -1). Find two pairs of polar coordinates (r, 0) for each point, one with r>0 and the other with r<0 . Express in radians.

 [Jun 5, 2006 5:03:06 PM] [Link]
pskinner

Joined: Apr 2, 2005
Posts: 797
Status: Offline
 Re: PRECAL HELP!!! Reply to this Post Reply with Quote

This is a trig question.

The point (1,-1), connected to (0,0), makes an angle with the x-axis of -pi/4.

Drop a perpendicular from (1,-1) to the x-axis and draw the triangle in in the fourth quadrant. Now, you can compute r=sqrt(2)/2, using pythagoras. So, one point in polar coordinates is:

(sqrt(2)/2,-pi/4).

That's when r is positive. If r is negative with the same angle, the point gets rotated 180 degrees around the origin, so to get it back the angle needs to be 180 degrees in the other direction, so the other point is:

(-sqrt(2)/2,3pi/4)
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Principal Skinner
 [Jun 5, 2006 8:31:09 PM] [Link]
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