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Almost a year ago, I wrote a post on How to hide all the edges of an object. Although what it's there is still valid if that is what you need, there is a much better way to do this.
You simply need to select the geometry you want to hide the edges of, and go to Window --> Soften Edges. This will bring the smooth soften edges dialog box to the screen, where you can play with the options of how to soften (hide) those edges.
As a quick example see how this surface created with Soap Skin Bubble, was soften to show how I wanted.
What you need to understand though, is that you are not just hiding the edges, you are joining the two faces too. The resulting surface will be one.