Finding angles in a trapezoid

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Taught by mrbrianmclogan
  • Currently 3.0/5 Stars.
6482 views | 1 rating
Part of video series
Meets NCTM Standards:
Errors in this video:

At 20 seconds, the teacher says that the expressions 3y + 40 and 3x - 70 are equal, but actually they are supplementary, so (3y + 40) + (3x - 70) = 180. Again at 2:35, he says that 3y + 40 = 110, but because the angle are supplementary, you should have 3y + 40 + 110 = 180.

Lesson Summary:

In this lesson, we learn how to find angles in a trapezoid by using alternate interior and corresponding angle theorems. The instructor takes us through a step-by-step process of finding the value of y and x in the given problem. By extending parallel lines and transversals, we can use same side interior angles to calculate the missing angles. By the end of the lesson, we have learned how to solve for variables and angles in a trapezoid.

Lesson Description:

Finding the values of variables to find angles in a trapezoid by using alternate interior and corresponding angle theorems.

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Questions answered by this video:
  • How do you find the angles in a trapezoid?
  • If 3 angles in a trapezoid are 120, x, and 3y + 40, and the the angles 3y + 40 and 3x - 70 are supplementary, what do x and y equal?
  • Why are the two angles on the side of a trapezoid supplementary?
  • How can you solve for x and y in a trapezoid when the angles are variable expressions?
  • Staff Review

    • Currently 3.0/5 Stars.
    This lesson shows how to solve a geometry problem for x and y when you are given a trapezoid with some angle measures given as variable expressions. The method used to solve for x and y is to use the expressions and your knowledge of trapezoids to solve for the unknown variables and finally the angle measures. All steps are explained.