Glencoe Math: Course 3, Volume 2
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Exercise 8 Page 408

Use the relationship of vertical angles between lines that intersect.

123^(∘)

Practice makes perfect

Let's consider the given diagram.

angles

To find the measure of ∠ 6, we will first find m∠ 1. Recall that when two lines intersect, vertical angles are formed on opposite sides of the point of intersection, and these angles are always congruent.

angles
Congruent angles have the same measure, so the measure of ∠ 1 is 80^(∘).
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Now, note that ∠ 2 and the angles with measure 80^(∘) and 43^(∘) form a straight line.

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Therefore, the sum of their measures is 180^(∘). With this information, we can find the measure of ∠ 2. m∠ 2+43^(∘)+80^(∘)=180^(∘) ⇕ m∠ 2=57^(∘) Let's add this information to our diagram.

angles

Next, we will find the measure of ∠ 3. We can use the fact that corresponding angles between parallel lines are congruent.

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Since ∠ 2 and ∠ 3 are corresponding angles, they are congruent and therefore have the same measure. This means that m∠ 3 = 57^(∘). Let's add this information to our diagram.

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Finally, note that ∠ 6 and ∠ 3, that measures 57^(∘), form a straight line.

angles

These angles are supplementary and therefore the sum of their measures is 180^(∘). With this information, we can find the measure of ∠ 6. m∠ 6+57^(∘)=180^(∘) ⇕ m∠ 6=123^(∘)