
Start with the given leg L and angle A 

1 
Draw a long horizontal line 

2 
Mark a point A towards the left end of that line. 

3 
Draw an arc across the given angle A. 

4 
Without changing the compass width, draw a similar arc on the line at A 

5 
Set the compass width to the width of the given angle A 

6 
With the same compass width, draw an arc across the previous one at A 

7 
Draw a long line from A through the point where the arcs intersect. 

8 
Set the compass width to the length of the given leg L 

9 
Without changing the compass, draw an arc from A across the horizontal line, creating point C 

10 
Set the compasses on C 

11 
Adjust the compass width to any medium setting 

12 
Draw two arcs across the horizontal line, creating points P and Q 

13 
With the compass at any medium width, from P and Q draw intersecting arcs above and below the line. 

14 
Using the straight edge, draw a line through where the two arc pairs intersect. Make it long enough to cross the top line, creating point B 


Done. ABC is a right triangle with the given leg L and given angle A 
