When two lines intersect, the opposite angles form vertical angles or vertically opposite angles. They are called vertical angles because they share the same vertex.The Vertical Angle Theorem states that
Vertical angles are equal.
Notice also that x and y are supplementary angles i.e. their sum is 180°.
The following diagram shows the vertical angles formed from two intersecting lines. Scroll down the page for more examples and solutions.
The following diagram shows another example of vertical angles.
The following video explains more about vertical angles.
Very often math questions will require you to work out the values of angles given in diagrams by applying the relationships between the pairs of angles.
Given the diagram below, determine the values of the angles x, y and z.
Solution:Step 1: x is a supplement of 65°.
Answer: x = 115°,
= 65° and z = 115°
Both AEC and DEB are straight lines. Find q.
∠AEB = ∠DEC ← vertical angles
q + 45˚= 135˚
q = 135˚ – 45˚ = 90˚
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