It is not that easy to draw a triangle in InDesign as you like it. If you wish to draw a triangle you select the polygon tool, you click once in the document page and you set the number of sides to three. But there is still the issue of how you set the angle of your triangle. Another way of drawing a triangle is by drawing a different shape, a e.g. rectangle or ellipse, and to convert this shape to a triangle. To do this select the shape and click on Object > Convert Shape > Triangle. This, however, still does not offer a way of setting the angle of your triangle. You can try to create the triangle of your choice by transforming it using the buttons you see on the picture. It is not that easy to use these tools effectively though. Especially if you want to make a right-angle (90°) that fits the contours of your document page exactly. To achieve this there is a little trick you can use. Draw a rectangle (it does not yet have to be the preferred size, hight and width) then use the Pen Tool (press P) and click on one of the corners. This corner will be deleted and you will have the perfect right-angled triangle. Select the object and use the arrows to decide the width and height of your triangle.
Featured Image: https://www.flickr.com/photos/ragesoss/369389643
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