Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
3. Proving Lines Parallel
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Exercise 34 Page 162

x=1.25
m∠1=10
m∠2=10

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&= 20-8x m∠2&= 30-16x 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 (20-8x)^(∘) and (30-16x)^(∘) 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. (20-8x)^(∘)= (30-16x)^(∘) Let's solve the equation for x.
20-8x=30-16x
20+8x=30
8x=10
x=1.25
Finally, we can use the fact that x=1.25 to determine the measures of ∠1 and ∠2. m∠1&=20-8( 1.25)=10 m∠2&=30-16( 1.25)=10 For x=1.25 we have that r ∥ s, m ∠ 1 = 10, and m ∠ 2 = 10.