Determine if the graph is symmetric about the x-axis, the y-axis, or the origin. r = 2 cos 5θ

Question

I would like for someone to explain how to do this. I don't want just an answer. My guess would be about the x-axis because there is a cosine but I don't think this a correct method to find out the answer. Please give a detailed explanation. 

Answer 1

All fundamental cosine are graphs symmetric about the y-axis.