These drawings, from my book Architectural Drafting for Interior Designers, show how to draw multiple parallel, angled lines using two triangles. This technique also works to draw perpendicular lines. Handy for when you don’t have an adjustable triangle.
Align a triangle with the line you wish to draw lines parallel to. In this case, the line is the wall the door is on.
Brace the triangle with a second triangle. You can also brace it with a scale.
Slide the first triangle back and forth on the second one to draw parallel lines. Or to draw lines perpendicular to the line the first triangle was aligned with.