Find the intersection between graph r=1 and r=2cosθ

i did cosθ= 1/2

cos^-1 1/2 = 1/3π (radiance)

from here on ward i was told to add something to this which should give me 5/3π

and thus my 2 intersection should be

(1, 1/3π) (1, 5/3π)

please tell me what i do in order to get to 5/3π

YEEEEEET Feb 27, 2019

#1**+2 **

Set the r's equal and we have that

2cos θ = 1 divide both sides by 2

cos θ = 1/2

arccos (1/2) = θ

Remember that arccos has a range of [-pi,2, pi/2 ]

Note that this happens at pi/3 and at -pi/3 = 5pi/3 if we are on the interval [0, 2pi ]

So...the intersection points are

(r, θ) = ( 1, pi/3) and (1, 5pi/3 )

CPhill Feb 27, 2019