First of all, Construct a line segment AB of 3cm. Then, from A construct a line AX measuring 120�. Keep your compasses on A and construct an arc of 3cm on the ray AX. Join the arc with B to get the desired triangle. To bisect it, there are 2 methods,1st : Measure 60�(120/2=60) with a protractor and draw it.2nd : Bisect 120 by:With A as center, and any radius, draw an arc intersecting the arms of AX and Mark them however you want for instance, we'll name it as EF. With radius more than 1/2 of EF Construct an arc on both the sides respectively. Join A with the arc made to obtain 60�!Sorry but I couldn't make it much simple as if I was in front of you.

The Construction:

To draw a triangle ABC with angle A measuring 120 degrees and AB = AC = 3cm, follow these steps:

1. Draw a line segment AB of length 3cm.
2. Place the compass at point A and draw an arc with a radius of 3cm to intersect the line segment AB. Label this point as C.
3. Now, draw another arc with the same radius of 3cm, centered at point C, to intersect the previously drawn arc. Label this point as B.
4. Join points A and C with a straight line segment. You have now formed triangle ABC with angle A measuring 120 degrees and AB = AC = 3cm.

The Bisector of Angle A:

To draw the bisector of angle A, follow these steps:

1. Draw an arc from point B, cutting the ray AC at a point. Label this point as D.
2. With D as the center, draw another arc that intersects the ray AC and the line segment AB. Label this point of intersection as E.
3. Join points A and E. This line AE is the bisector of angle A.

Explanation:

The given triangle ABC has angle A measuring 120 degrees and sides AB and AC equal to 3cm. By following the construction steps, we have successfully drawn triangle ABC. Now, let's understand the construction of the bisector of angle A.

To construct the bisector of angle A, we used the property that the bisector of an angle divides it into two equal angles. We started by drawing an arc from point B, intersecting the ray AC at point D. Then, with D as the center, we drew another arc that intersected the ray AC and the line segment AB at point E.

The line AE is the bisector of angle A. It divides angle A into two equal angles, each measuring 60 degrees. This is because the two angles formed at E, i.e., angle EAB and angle EAC, are congruent. Thus, the line AE acts as a dividing line, evenly splitting angle A into two equal parts.

The bisector of angle A is an important line in triangle ABC as it helps in various geometric constructions and calculations related to triangle ABC.