How do you graph the polar equation #1=rcos(theta-pi/6)#?

1 Answer
Mar 19, 2018

To graph this easily, we can convert it to rectangular form.

In order to convert, we need to the cosine angle difference formula:

#cos(color(red)A-color(blue)B)=coscolor(red)Acoscolor(blue)B+sincolor(red)Asincolor(blue)B#

Knowing that #rsintheta=y# and #rcostheta=x#, we can convert:

#1=rcos(theta-pi/6)#

#1=r(costhetacoscolor(black)(pi/6)+sinthetasincolor(black)(pi/6))#

#1=r(costheta*sqrt3/2+sintheta*1/2)#

#1=rcostheta*sqrt3/2+rsintheta*1/2#

#1=x*sqrt3/2+y*1/2#

#1-x*sqrt3/2=y*1/2#

#2-x*sqrt3=y#

#y=2-x*sqrt3#

#y=-sqrt3 x+2#

Now we can graph this linear equation like any other line.

An easy strategy would be to solve for the #x#- and #y#-intercepts, then connect the dots.

The #x#-intecept occurs when #y=0#, so:

#color(white)=>y=-sqrt3 x+2#

#=>0=-sqrt3 x+2#

#color(white)=>sqrt3 x=2#

#color(white)=>x=2/sqrt3#

#color(white)=>x=(2sqrt3)/3#

This means that the #x#-intercept is at #((2sqrt3)/3,0)#. Call this point #A#. The #y#-intercept occurs when #x=0#, so:

#color(white)=>y=-sqrt3 x+2#

#=>y=-sqrt3 *0+2#

#color(white)=>y=2#

This means that the #y#-intercept occurs at #(0,2)#. Call this point #B#. Now that we have our two points, we can graph the line:

https://www.desmos.com/calculator

That's it. Hope this helped!