Categories
Intermediate

Ceteris paribus

Three circles with their centres and a triangle ABC. Given that D is the midpoint of BC, prove that quadrilateral ABEF and triangle ECF have both equal perimeter and equal area.

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Advanced

Slightly skewed

Two overlapping equilateral triangles with side lengths 1. What is the total red length?

Categories
Beginner

The green field

A square is divided in two quadrilaterals of given area. What fraction of the square’s perimeter is red?

Categories
Advanced

The Post-it note

Two unit squares (having side 1) are placed as shown. What is the total perimeter of the two red triangles?