## 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.