Maybe we are not working from the same start position.

  1. Select QuickShape Tool.
  2. Create Polygons.
  3. Number of sides: 3.
  4. Ctrl+Drag to 400px and 270deg or type in the same.
  5. Create a horizontal Guide line through the leftmost vertex.
  6. Place the mouse over the right side on the guide and when the cursor changes to an arrowhead, click-drag the curve along the guide to maintain symmetry.
  7. Change the rotation to 0deg.

Acorn