Question

in the triangular pyramid shown below, which lines are skew?
cf and df
cf and de
ce and de
cf and ef

Explanation:

Step1: Recall skew - line definition

Skew lines are non - parallel and non - intersecting lines in 3 - D space.

Step2: Analyze each option

• $\overleftrightarrow{CF}$ and $\overleftrightarrow{DF}$ intersect at point $F$, so they are not skew.
• $\overleftrightarrow{CF}$ and $\overleftrightarrow{DE}$ are non - parallel and do not intersect. They are in different planes.
• $\overleftrightarrow{CE}$ and $\overleftrightarrow{DE}$ intersect at point $E$, so they are not skew.
• $\overleftrightarrow{CF}$ and $\overleftrightarrow{EF}$ intersect at point $F$, so they are not skew.

Answer:

$\overleftrightarrow{CF}$ and $\overleftrightarrow{DE}$