Three identical equilateral triangles overlap as shown. Find the length AB.
What can you work out that is not labelled?
Identical triangles have equal base lengths.
The first and second triangles begin 18 cm apart. Because their bases are equal, their right endpoints are also 18 cm apart. That second 18 cm is present even though it is not labelled.
The 41 cm span contains that hidden 18 cm and most of the third triangle’s base. Add back the 3 cm overlap to obtain one complete base.
AB = 41 − 18 + 3 = 26 cm
AB equals the base because the triangle is equilateral.
Did the reveal make it feel easier?
Understanding a relationship after someone highlights it is valuable. Discovering one independently in the next unfamiliar question is another ability to practise.
Seeing Math means looking beyond what is given to discover hidden information and relationships that reveal a possible first step.

