Question Video: Identifying Alternate Exterior Angles Mathematics • 8th Grade

Video Transcript

Find the value of 𝑥 in the figure.

We can start this question by identifying some key information we are given. Firstly, by the markings on the lines, we observe that we have two parallel lines. This third line can be considered as a transversal of these parallel lines. As we need to find the unknown angle measure of 𝑥 degrees, let’s recall some angle facts about the angles created between two parallel lines and a transversal.

We’re very used to seeing the angles in parallel lines drawn in nice horizontal lines like this. The congruent angles, which include corresponding, alternate interior, and alternate exterior angles, can be represented as shown. So, sometimes, when the parallel lines aren’t horizontal or even vertical, it may be difficult to work out any congruent or supplementary angle measures.

But if we consider the angles of measure 𝑥 degrees and 124 degrees, these are a pair of alternate exterior angles. And therefore, they will be equal in measure. We can give the answer that 𝑥 is 124. Note that we don’t need to include the degree symbol, as the unknown angle was defined as 𝑥 degrees, which would be 124 degrees.