Pearson Geometry Common Core, 2011
PG
Pearson Geometry Common Core, 2011 View details
3. Proving Lines Parallel
Continue to next subchapter

Exercise 33 Page 162

x=2.5
m∠1=30
m∠2=30

Practice makes perfect

We want to determine the value of x for the given measures of angles for which r∥ s. In this case, we have been given expressions to represent the measures of ∠ 1 and ∠ 2. m∠1&= 40-4x m∠2&= 50-8x Let's add these angle measures to the given figure so that we can get a better idea of their relationship.

We can see that (40-4x)^(∘) and (50-8x)^(∘) are corresponding angles. Because we want to determine the measures of the angles for which the lines r and s will be parallel, we will use the Converse of the Corresponding Angles Theorem to determine x.

Converse of the Corresponding Angles Theorem

If two lines and a transversal form corresponding angles that are congruent, then the lines are parallel.

We can visualize this theorem. Consider two lines l and m. These lines are parallel if one of the following pairs of angles form a pair of corresponding congruent angles.

Applying the theorem, we can create an equation using the fact that the corresponding angles must be congruent for the lines r and s to be parallel. (40-4x)^(∘)= (50-8x)^(∘) Let's solve the equation for x.
40-4x=50-8x
40+4x=50
4x=10
x=2.5
Finally, we can use the fact that x=2.5 to determine the measures of ∠1 and ∠2. m∠1&=40-4( 2.5)=30 m∠2&=50-8( 2.5)=30 For x=2.5 we have that r ∥ s, m ∠ 1 = 30, and m ∠ 2 = 30.