Final answer:
To find BC, apply the segment addition postulate. BC is half the length of AC, which is 4x - 10.
Step-by-step explanation:
Segment Addition Postulate in geometry to find the length of segment BC when it is given that point B is the midpoint of segment AC and the length of AC is given by the equation 8x - 20. Since B is the midpoint, AB is equal to BC. Therefore, we set up the equation AB + BC = AC and substitute AB and BC with BC, and AC with 8x - 20.
In this case, AC is given as 8x - 20. So, BC would be half of AC: BC = (8x - 20)/2 = 4x - 10.