How To Get A Triangle Shape/Vector in Adobe InDesign

Click the Polygon tool on the toolbar.

Then Double Click with your mouse. The following setting will pop up. Put 3 for “Number of Sides”, and 0% for “Start Inset”

Then place on the document.

Viola! You have a triangle.

Alternate Way

A second way to do a vector triangle, and other vector elements with more complicated shapes. You can first do them in Adobe Illustrator and then copy and paste into Adobe InDesign. It will retain its vector qualities.