Answer: 6cm.
Step-by-step explanation:
To construct the line B to D:
1. Open your compass to a specific length. (Ideally record this length using a ruler to measure it) eg. 5cm.
2. Place the point of your compass on B and draw small arc that cuts the line from B to A. (Label his point E)
3.Using the same compass length (ie. for this example: 5cm), place your compass on point B again and draw another small arc, this time cutting the line from B to C. (Label this point F)
4. Now you have a point on line BA and another point on line BC.
5. Adjust compass length (or keep it the same length ie. 5cm if it suits). If you adjust the length at this point then make sure that it is the same length for the next two steps.
6. Placing the point of your compass on point E, draw a large arc that spans the area of the angle.
7. Repeat this process for point F.
8. Ensure that both of the arcs drawn in steps 6 & 7 intersect each other at a point.
9.Draw a line from B to the point of intersection of the two arcs drawn in steps 6 & 7.
10. Then, using a ruler, measure 4cm on this new line from point B. Label this 4cm mark as point D.
11. Finally, connect point C to D using a ruler and measure its length.
