Converting Coordinates from Rectangular to Polar
Key Questions
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Let's look at the trig formulas SYR, CXR, TYX:
sin theta = y/r
cos theta = x/r
tan theta = y/x Since we are given the Cartesian coordinates, we are given
x andy . For polar coordinates, we need to figure outr andtheta .r is easy, we just use Pythagorean:r=sqrt(x^2+y^2) To figure out
theta , I like to use cosine because the range of arccosine is in quadrants I and II and adjustingtheta' is easier. So,theta'=cos^(-1)x/r If
y>=0 thentheta=theta' .
Ify<0 thentheta=2 pi - theta' (in radians) ortheta=360-theta' (in degrees).Our final answer is
(r, theta) .Let's look at a concrete example: Convert
(-3, 3sqrt3) to polar coordinates:r=sqrt((-3)^2+(3sqrt3)^2)=sqrt(36)=6
theta'=cos^(-1)((-3)/6)=(2pi)/3
y<0 so,theta=2pi-(2pi)/3=(4pi)/3 So the polar coordinates are
(6, (4pi)/3) . -
I presume we're looking for a radius
r and angletheta such thata + bi = r(cos theta + i sin theta) .Pythagoras theorem gives us
r = sqrt(a^2+b^2) .Simple trigonometry gives us
tan theta = b/a , sotheta = arctan (b/a) .