Given two parallel lines
Calculate the angle
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Given two parallel lines
Calculate the angle
The angle 125 and the angle alpha are vertically opposite angles, so they are equal to each other.
If one of two corresponding angles is a right angle, then the other angle will also be a right angle.
Vertically opposite angles are formed when two lines intersect. They're the angles that are across from each other, not next to each other. In this diagram, α and 125° are on opposite sides of the intersection point.
The parallel lines don't change that α = 125°! Whether lines are parallel or not, vertically opposite angles are always equal. The parallel lines create other angle relationships, but not for these two specific angles.
Look for angles that are across from each other when two lines cross. If you drew an 'X', vertically opposite angles would be at the opposite ends of each line in the X.
Supplementary angles are adjacent (next to each other), not opposite! Since α and 125° are vertically opposite, they're equal, not supplementary. Adjacent angles at an intersection are supplementary.
Look for key words: if the problem mentions angles being 'vertically opposite' or 'across from each other', they're equal. If they're 'adjacent' or 'next to each other', they add to 180°.
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