In the figure X is any point in the interior of triangle. Point X is joined to vertices of triangle. Seg `PQ||` set DE, set `QR||` set EF. Fill in the blanks to prove that set `PR||` seg DF.

Answer

In `DeltaXDE, PQ abs() DE`
`therefore " " (XP)/(PD) = (XQ)/(QE)`
In `DeltaXEF, QR abs() EF`
`therefore" " (XR)/(RF) = (XQ)/(QE)`
`therefore " "(XP)/(PD) = (XR)/(RF)`
`therefore` seg PR `abs()` DF