Final answer:
To find the length of DE, we use the concept of midpoint. Since E is the midpoint of DF, DE is equal to EF. Therefore, the length of DE is 8x+40.
Step-by-step explanation:
The concept of midpoint and equal lengths is fundamental in geometry and refers to the relationship between points or line segments. To find the length of DE, we need to use the concept of midpoint. The midpoint divides a line segment into two equal parts. Since E is the midpoint of DF, we can write the equation DE = EF. The length of DF is given as 8x+40. Therefore, the length of DE is also 8x+40.