To construct the angle bisector of ∠ABC using only a ruler and compass, follow these steps:

Step-by-Step Construction:

1. Draw the Angle:
   Start by using the protractor to draw ∠ABC with the given angle of 70°.

2. Mark an Arc Across Both Rays:

   • Place the compass point at point $B$ (the vertex of the angle).
   • Set the compass to a moderate width and draw an arc that intersects both arms $BA$ and $BC$.
   • Label the points of intersection as $D$ (on $BA$) and $E$ (on $BC$).

3. Construct an Arc Between $D$ and $E$:

   • Without changing the compass width, place the compass point on $D$ and draw an arc within the angle.
   • Repeat the same with the compass point on $E$, creating an intersection with the previous arc. Label this intersection point as $F$.

4. Draw the Angle Bisector:

   • Use the ruler to draw a straight line from $B$ through $F$. This line is the bisector of ∠ABC.

This method ensures that all construction lines are shown and the bisector is accurate.

Would you like further clarification or additional examples? Let me know!

Questions to Expand Understanding:

1. Why is it necessary to keep the compass width unchanged between steps 3 and 4?
2. How can you verify that the constructed line is indeed the angle bisector?
3. What are the differences between bisecting an angle and a line segment?
4. Could the process be adapted to bisect a reflex angle (greater than 180°)?
5. What would change if the given angle was obtuse instead of acute?

Tip:

Always ensure your compass is tightly fixed to avoid accidental changes in width during the construction.