## Finding angles in a trapezoid

Finding angles in a trapezoid
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6213 views, 1 rating - 00:04:40
Part of video series Solving for Angle Measures
Taught by mrbrianmclogan

### Meets NCTM Standards:

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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.
Finding the values of variables to find angles in a trapezoid by using alternate interior and corresponding angle theorems.
• 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?
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.
• Currently 3.0/5 Stars.
Reviewed by MathVids Staff on January 15, 2012.  