Midpoint theorem

The line joining the midpoints of two sides of a triangle is parallel to the third side and half its length. CAPS Grade 10 definition, worked example and related geometry practice.

The line joining the midpoints of two sides of a triangle is parallel to the third side and half its length.

Definition

The midpoint theorem says that in any triangle, the line segment joining the midpoints of two sides is parallel to the third side and equal to half of its length. Its converse says that a line through the midpoint of one side, parallel to a second side, bisects the third side.

Worked example

In △ABC, D and E are the midpoints of AB and AC. If BC = 14 cm, then DE ∥ BC and DE = 7 cm.

Joining the midpoints of the sides of any quadrilateral forms a parallelogram, which you can prove with the midpoint theorem twice.

Where it appears in the exam

Midpoint theorem is part of the geometry section of CAPS Grade 10 Mathematics and is examined in Paper 2 of the November exam.

Step-by-step method

  1. Check that the points are midpoints of two sides of the same triangle.
  2. State DE ∥ BC (midpoint theorem).
  3. Use DE = ½BC to find the length.
  4. Write 'midpt theorem' as the reason.

Common mistake

Using the theorem when the points are not midpoints of the sides.

Related geometry terms

Frequently asked questions

What does midpoint theorem mean in Grade 10 Maths?

The midpoint theorem says that in any triangle, the line segment joining the midpoints of two sides is parallel to the third side and equal to half of its length. Its converse says that a line through the midpoint of one side, parallel to a second side, bisects the third side.

Which paper tests midpoint theorem in Grade 10?

Midpoint theorem belongs to the Geometry section of CAPS Grade 10 Mathematics, which is examined in Paper 2 of the November exam.

How do I practise questions involving midpoint theorem?

Snap a question that uses midpoint theorem into Snap&Learn with your grade set to Grade 10, or work through the Grade 10 topic guide and practice papers.

Snap&Learn gives South African Matric learners instant, CAPS-aligned, step-by-step Mathematics solutions. Snap or upload a question and the AI shows every method mark the way the NSC memo awards them. Your first three AI solutions are free.