~ 7.5 ~

Using Equations to Solve for Unknown Angles

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Learning Targets

I can write an equation to represent a relationship between angle measures and solve the equation to find unknown angle measures.

Notes

To find an unknown angle measure, sometimes it is helpful to write and solve an equation that represents the situation. For example, suppose we want to know the value of in this diagram.

Using what we know about vertical angles, we can write the equation 3x + 90 = 144 to represent this situation. Then we can solve the equation.

3x + 90 = 144

3x + 90 - 90 = 144 - 90

3x = 54

divide by 3

x = 18

Create equations to solve for missing angles (practice) | Khan AcademyUse understanding of vertical, complementary, and supplementary angles to set up an appropriate equation to solve for a missing angle measure.

Unknown angle problems (with algebra) (practice) | Khan AcademyPractice setting up algebraic equations to solve unknown angle problems.

Activities

5.2 What Does It Look Like?

Elena and Diego each wrote equations to represent these diagrams. For each diagram, decide which equation you agree with, and solve it. You can assume that angles that look like right angles are indeed right angles.