diagonal lines always jagged

How can you make diagonal lines that have crisp smooth edges? I'm working on a business logo, and the logo has a triangle in it. How can i make the triangle with smooth edges?

If you are working with logos you really should be working in vector. (IE: Illustrator). Its makes much smoother graphics and it resizeable. You can make it as big or as little as you want and it won't pixelate.

However to make smoother objects in photoshop you generally have to turn 'anti-aliass' on.

You can create perfectly smooth vector shapes in Photoshop using the Polygon Tool. Select the Polygon Tool in the toolbox, set it to either 'Shape layers' or 'Paths' in the Tool Options Bar, then set the number of sides to 3 in the Tool Options bar. You can then drag in your image to create a triangle of any size.