How to find missing angle of a Triangle or Parallel Lines Cut By A Transversal.

How to find a missing angle of a triangle or parallel lines cut by a transversal.

​Finding a missing angle in a triangle.

​Watch and then answer:

​What is the first step in finding a missing angle?

​

​1) All interior angles = 180.

​2) So, we can add all the angles together, even with variables, and set them equal to 180.

​

​x + 10 + 2x + 20 + 2x - 5 = 180

​Combine like terms:

all variables the same. 1x + 2x + 2x = 5x

all constants. 20 + 10 - 5 = 25

​

​Your new equation: 5x + 25 = 180

​ subtract the constant - 25 -25

​ 5x = 155

divide both sides by 5 to isolate the variable.

​ 5x/5 = 155/5

x=31

​Check Your Work:

​Replace all x's with (31) and see if both sides are equal.

​5x + 25 = 180

​5 (31) + 25 = 180

​Use your calculator

​180 = 180

​This proves 31 is the

​answer for x.

​Solving Two Step Equations: Check

your answer.

​To check your answer, put your value of x into the equation in place of the x.

​10(2) + 15 = 35

​20 + 15 = 35

​ 35 = 35

​This proves your answer for k is true.

​Use the video in today's folder

​that says tutorial for ​Parallel Lines Unit 2B.