Module 25  Polar Functions 
Introduction  Lesson 1  Lesson 2  Lesson 3  SelfTest 
Lesson 25.1: Polar Coordinates 
Polar coordinates are an alternative way of identifying points in a plane. They are useful in many applications and for certain types of regions and curves because functions given in polar coordinates can be simple to use. Polar coordinates will be explored in this lesson and you will learn how to convert points given in rectangular coordinates to polar coordinates and viceversa. Defining Polar Coordinates When assigning rectangular coordinates (x, y) to a point P in the plane, x is the horizontal distance and y is the vertical distance from the origin O to the point P. If polar coordinates (r, ) are used instead, r is the directed distance from the origin O to the point P and is the directed angle from the positive xaxis to ray OP. Recall that polar coordinates are not unique. In fact, there are infinitely many possible polar coordinates for any point in the plane. Converting Rectangular Coordinates to Polar Coordinates The TI89 has features that convert coordinates from rectangular to polar and viseversa. Use the TI89 to find a value of r for the point (3, 2).
This item returns the value of r in one of the possible polar coordinates for a point given in rectangular coordinates.
The distance from the origin O to the point P is , so the polar coordinate r is . Find a value of for this point.
The rectangular point (3, 2) is represented as ( , arctan (2/3)), or approximately as (3.61, 0.588) in polar coordinates. Because the calculator is in Radian mode, the angle is given in radians. 25.1.1 If (r, ) are polar coordinates for a point P, what are the other possible polar coordinates for P? Click here for the answer. Converting from Polar to Rectangular Coordinates 25.1.2 Use the and features in the Math Angle menu to find the x and ycoordinates for the polar point . Click here for the answer. The rectangular coordinates for a point are unique. 
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