Estimate the length of the midline of triangle ABC, which is parallel to side AB, if 10.4.

We will use the well-known property of the middle line of a triangle, namely, that. which for on the midline of any triangle is equal to half the length of that side of this triangle that is parallel to this midline.

In the initial data for this task, it is reported that the length of the side AB of the triangle ABC satisfies the following double inequality:

10.4 <| AB | <10.5.

Dividing all parts of this double inequality by the number 2, we get:

10.4 / 2 <| AB | / 2 <10.5 / 2;

5.2 <| AB | / 2 <5.25.

Therefore, the length of the centerline of this triangle, which is parallel to the side AB, is greater. than 5.2 and less than 5.25.

Answer: the length of this midline is greater. than 5.2 and less than 5.25.