Question

In Fig., a transversal n cuts two lines l and m. If ∠1 = 70° and ∠7 = 80°, is l || m?

Answer 1

We know that if the alternate exterior angles of two lines are equal, then the lines are parallel.
In the given figure, $\angle 1\mathrm{and}\angle 7$ are alternate exterior angles, but they are not equal.
$$\begin{gathered} \angle 1\ne \angle 7 \\ 70°\ne 80° \end{gathered}$$

Therefore, lines l and m are not parallel.