Question: plotting trig functions. unexpected behavior

I'm a calulus 1 student, using Maple to help write my homework assignments. I came across this problem I'm having with Maple 18.

I'm working on explaining analytically where the veriticle asymptotes occur on f(x) = cos*x/(x^2+2*x);

I get all of it done, and at the end I want to insert a plot of this function to finish my disussion.

 

This is very surprising to see Maple behave this way. What am I doing wrong? Or why is Maple not plotting a simple graph accuratly??

 

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