GCSE Secondary Maths Age 13-17 - Algebra: Cosine Rule - Explained

The video tutorial explains how to prove that line AC is equal to line BD in a quadrilateral ABCD, where AB equals CD and angle ABC equals angle BCD. The teacher separates the quadrilateral into two triangles, ABC and BCD, to demonstrate congruency using the side-angle-side condition. By proving the triangles congruent, it is concluded that AC equals BD. The tutorial also highlights the importance of identifying common elements and reviews the four conditions of congruency.

What is the relationship between AB and CD in the quadrilateral ABCD?

Explain how angle ABC relates to angle BCD.

What must be proven about the lines AC and BD?

Describe the process of separating the triangles in the proof.

What is the significance of BC being common in both triangles?

How does proving the triangles are congruent lead to the conclusion that AC is equal to BD?

List the conditions of congruency mentioned in the proof.