Big Ideas Math: Modeling Real Life, Grade 8
BI
Big Ideas Math: Modeling Real Life, Grade 8 View details
2. Angles of Triangles
Continue to next subchapter

Exercise 7 Page 114

The angles inside a triangle are called interior angles.

∠ J = 40^(∘), ∠ Y = 20^(∘)

Practice makes perfect
We can draw a triangle between Jamestown, Williamsburg, and Yorktown. Let's look at the map!
Draw the Historic Triangle
We are given that the interior angle at Williamsburg ∠ W measures 120^(∘) and that the interior angle at Jamestown ∠ J is twice the measure of the angle at Yorktown ∠ Y. We can write the measurements for ∠ J and ∠ Y in terms of the variable x using the given relationship. m∠ W = 120^(∘) , m∠ J= 2x^(∘) , and m∠ Y = x^(∘)

Recall that interior angles of a triangle are the angles inside that triangle. With this information, we can mark the angles ∠ W, ∠ J, and ∠ Y on the diagram.

Mark angles on the Historic Triangle

Next, we can find the measure of the interior angles at Jamestown and Yorktown. We will do this using the rule for the interior angle measures of a triangle.

Interior Angle Measures of a Triangle

The sum of the interior angles of a triangle is 180^(∘).

Using this rule, we can write the equation for the interior angles of the given triangle. 120^(∘) + 2x^(∘)+ x^(∘)=180^(∘) Now, let's solve the equation for x.
120 + 2 x + x = 180
120 + 3 x = 180
3 x = 60
x = 20
We found that x=20. This means that the measure of interior angle at Yorktown is 20^(∘). We can substitute 20 for x to evaluate the expression for the interior angle at Jamestown.
2x^(∘)
2( 20)^(∘)
40^(∘)
The measure of the interior angle at Jamestown is 40^(∘).