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# and#y# . For polar coordinates, we need to figure out#r# and#theta# .#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 adjusting#theta'# is easier. So,#theta'=cos^(-1)x/r# If
#y>=0# then#theta=theta'# .
If#y<0# then#theta=2 pi - theta'# (in radians) or#theta=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 angle#theta# such that#a + 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# , so#theta = arctan (b/a)# .