Vertically Opposite Angles

Move either Point A or Point C.
What do you notice about the 'blue' angles ABD and CBE?

What do you notice about the 'pink' angles ABC and DBE?
Use the 'Show Label' tool to measure these angles.

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You should find that angle ABD is equal to angle CBE
and that angle ABC is equal to angle DBE.

Angle ABD and angle CBE are called Vertically Opposite Angles because they are opposite each other on either side of a vertex, formed by the intersection of two straight lines.

Similarly, angle ABC and angle DBE are also vertically opposite angles.

Can you explain why vertically opposite angles are always equal?
(Hint: Try using the 'angles in a straight line' property. Return to the module for the answer!)

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