Answer:
Work on a grid, like a piece of paper with squares already drown in it, else you need to be really accurate with 90 degrees angles. Draw an horizontal line, count 5 units (cm, inches, squares, whatever you have and draw a piece of a circle (red in my image) that intersect the 4 unit line (green). Join the point you found with the center of the circle to get the angle you want (blue line, the angle is the one marked. Joining ANY point in the first line with any point in the second line will give you the triangle you want. The orange lines are a few possibilities you have.
Is it a bad drawing? Yes. I used paint with a grid made with a spreadsheet, don't expect a masterpiece.