I totally forgot how to do this and was wondering if someone could explain for me. I can't remember how to figure out the 130 degree angle in the picture i've put up.

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- Aug 25th 2008, 10:51 AMJonathanEyoonGeometry
I totally forgot how to do this and was wondering if someone could explain for me. I can't remember how to figure out the 130 degree angle in the picture i've put up.

- Aug 25th 2008, 11:02 AMJhevon
refer to the modified diagram below:

the blue angles are alternate interior angles, and so, have the same measure

the red angle is the third angle of a triangle. since the angles in a triangle add up to 180 degrees, this angle is equal to 180 - (the sum of the other 2 angles).

when it's all said and done, the desired angle is $\displaystyle \underbrace{180 - 50 - 32}_{\text{the angles in the triangle}} + \underbrace{32}_{\text{the lower blue angle}} = 130$