Answer:
∠A = 166°
Step-by-step explanation:
We can imagine the parallel line to the left as a shifted version of the one on the right. As we move it further left along the line the in middle (called a <em>transversal</em>), ∠B will slide closer and closer to ∠A. Eventually, the two will totally coincide, showing that ∠B ≅ ∠A. We call ∠A and ∠B <em>corresponding angles</em>, because they can be made to perfectly overlap in that way.
Since corresponding angles are congruent, their measures must be equal, so in this example, we can say that
, and since
and
,
To solve for <em>x</em>, we can subtract 3x and 40° from both sides:
and divide both sides by 4:
We can now replace <em>x </em>with 18° in our expression for ∠A to find