1, take a point o on any straight line AB;

2. Take point O as the center and any length as the radius, and make arc intersection point AB at two points C and D;

3. Take C and D as the center of the circle and any length as the radius, so that the two arcs intersect at a point E;

4. Connect OE, and then connect OE ⊥ AB;

5. take a little f from AB and connect FE.

Then △OEF is the right triangle to be made.