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 quadrilateral add up to 360 degrees
Angles on a straight line add up to 180 degrees
Opposite Angles Are Equal
Exterior angle of a triangle is equal to the sum of the opposite interior angles
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
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
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
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.