Videos and solutions to help Grade 8 students apply knowledge of geometry to writing and solving linear equations.

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Lessons for Grade 8

Common Core For Grade 8

• Students apply knowledge of geometry to writing and solving linear equations.

Lesson 5 Summary

• We know that an algebraic method for solving equations is more efficient than guessing and checking.

• We know how to write and solve equations that relate to angles, triangles, and geometry in general.

• We know that drawing a diagram can sometimes make it easier to understand a problem and that there is more than one way to solve an equation.

Classwork

Example 1

One angle is five less than three times the size of another angle. Together they have a sum of 143°. What are the sizes of
each angle?

Example 2

Given a right triangle, find the size of the angles if one angle is ten more than four times the other angle and the third
angle is the right angle.

Example 3

A pair of alternate interior angles are described as follows. One angle is fourteen more than half a number.
The other angle is six less than half a number. Are the angles congruent?

Exercises 1–6

For each of the following problems, write an equation and solve.

1. A pair of congruent angles are described as follows: the measure of one angle is three more than twice a number
and the other angle’s measure is 54.5 less than three times the number. Determine the size of the angles.

2. The measure of one angle is described as twelve more than four times a number. Its supplement is twice as large.
Find the measure of each angle.

3. A triangle has angles described as follows: the first angle is four more than seven times a number, another angle is
four less than the first and the third angle is twice as large as the first. What are the sizes of each of the angles?

4. One angle measures nine more than six times a number. A sequence of rigid motions maps the angle onto another
angle that is described as being thirty less than nine times the number. What is the measure of the angles?

5. A right triangle is described as having an angle of size “six less than negative two times a number,” another angle
that is “three less than negative one-fourth the number”, and a right angle. What are the measures of the angles?

6. One angle is one less than six times the size of another. The two angles are complementary angles. Find the size of
each angle.

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