Angle Facts for GCSE

To do well at GCSE maths you need to have a good grasp of the basic angle facts that underpin geometry. Thankfully we’ve got this handy guide for you which sets out all the basics you need to know. Master these rules and you’ll be fine.

Angles in a triangle add up to 180 degrees

Angles in a Triangle
The interior angles of any triangle add up to 180 degrees

Angles in a quadrilateral add up to 360 degrees

Angles in a Quadrilateral
The interior angles of any quadrilateral add up to 360 degrees

Angles on a straight line add up to 180 degrees

Angles on a straight line
a + b = 180 degrees

Opposite Angles Are Equal

Opposite Angles
Where two straight lines cross, the opposite angles are equal.

Exterior angle of a triangle is equal to the sum of the opposite interior angles

Exterior Angle of a Triangle
x = y + z

As the angles on straight line add up to 180 degrees and the three interior angles of a triangle also add up to 180 degrees, the exterior angle of a triangle is equal to the sum of the opposite two interior angles as shown above.

Working With Parallel Lines

Corresponding Angles are Equal

Corresponding Angles
Corresponding Angles

When you have a pair of parallel lines, with one line crossing them, the corresponding angles are equal. Basically the angles in the same position on each parallel line will be equal to the angle in that position on the other parallel line. This rule is sometimes remembered as “F angles” because the angles make an F shape. I know… it’s easiest to just see this one on the diagram.

Alternate Angles are Equal

Alternate Angles
Alternate Angles

Where you have two parallel lines, the alternate angles (as shown above) are always equal. This rule is sometimes remembered as “Z angles” because the angles make a Z shape.

Co-Interior Angles add to 180 degrees

Co-interior angles
Co-Interior Angles add to 180 degrees

Here is another rule where you have two parallel lines. This time the co-interior angles add up to 180 degrees. The rule is sometimes remembered as “C angles” because the angles make a C shape. You’re looking out for the angles on the same side of the line crossing the parallel lines, and on the inside (interior) of the parallel lines.

Those are the important basic angle facts that you need to know for GCSE maths, so make sure you learn them. Check out our resources page for more questions on this topic and others. You can also contact us for any specific support or to ask any questions.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top