Question

Find the angle ∠a for the below figure.

degrees.



Here the parallel lines are shown by arrow marks.

Answer 1

As the two black lines are parallel and the blue line is the transversal.
Hence, $\angle b$ and $\angle c$ are alternate interior angles.


$\therefore \angle b=\angle c={140}^o$(by alternate interior angle theorem)

Now, for the blue and green parallel lines, black lines are transversal.

Corresponding to the lower black line, $\angle c$ and $\angle a$ are alternate interior angles.
$\therefore \angle c=\angle a={140}^o$