# Very short question function composition?

I have to draw the plot of domain of the function z=(y+x)/cosx...so I have to draw the $x \neq k\pi +\pi/2$ graph..how do I do this? I tried replacing it by $\text{cos(x)} \neq 0$ but I dont know how to build this one either?

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$x\neq k\pi +\frac{\pi}{2}$ is no function, hence you have no graph, try to rephrase your question –  Dominic Michaelis Mar 12 '13 at 17:44

Your domain is comprised of infinitely-many pairwise-disjoint open strips. Draw the vertical lines $x=\pm\pi/2,$ $x=\pm3\pi/2,$ $x=\pm 5\pi/2$ (and so on) as dotted lines--at least, as many of these as will fit in the window of your graph--your domain will consist of every point in the plane that isn't on one of those dotted lines.