Explanation:
position your compass at point A and using the same distance mark arcs on line AB(mark the point it meets the line D)and AC(mark the meeting point of the arc and the line E).Place your compass at D and draw an arc at the middle of the angle,using the same measurements position your compass at point E and draw an arc.Where the two arcs meet label F using a ruler draw a straight line from F to meet point A.
Note;the width of the compass when making the arcs should be the same always