Angle Properties

Angle Properties

When we have multiple lines that cross each other we can use our maths skills to find angles at the intersections. Here are the angle properties that you should be aware of.

Angles on a Straight Line Add Up to 180°

If you have a straight line and one or more lines emerging from this line from a point at an angle, the angle(s) will add up to 180°. The diagram on the right shows this very well. The line emerges from the straight horizontal line. If you now were to add angle a and b together, they would equal 180°
Angles on a Straight Line

Vertically Opposite Angles are Equal

Another important angle property is that vertically opposite angles are equal. This means that angles opposite each other are the same. In the diagram on the left two lines cross each other. Each pair of opposite angles (a&b and c&d) is equal.
Vertically opposite angles

Alternate Angles are Equal

On the right you can see the alternate angle property. Alternate angles are angles in a Z shape. The rule is that both of these angles are equal as shown in the diagram (a and b). For this to be true, 2 of the lines have to be parallel and another line has to cross both parallel lines as in the example.
Alternate angles

Co-interior angles add up to 180°

Another angle rule is the co-interior angle property. As shown on the left, there have to be 2 parallel lines and one other line intercepting them. The angles in the C shape (a and b) add up to 180° as in the diagram.
Co-interior angles

Corresponding Angle Property

The corresponding angle property involves the angles in an F shape as shown on the right. There have two be 2 parallel lines and one line crossing them. As in the diagram, the angles of the F shape (a and b) are equal.

Looking at Shapes

Now you should know a lot about angles and their properties. Next, you should have a look at area and perimeter. You can also have a look in our library for other topics. Please share this page if you like it or found it helpful!
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Chapter 27.2:  Learning Outcomes Students will learn about different angle properties linked to parallel and intersecting lines!



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