Explanation:
ΔADG - NO (it's an equilateral triangle)
ΔAFH - NO (it's an equilateral triangle)
ΔBCH - NO (it's an equilateral triangle)
ΔBEH - NO (it's an equilateral triangle)
ΔBFG - YES
ΔCDG - YES
ΔEFG - YES
ΔDFG - NO (it's an equilateral triangle)
All equilateral triangles have the sides equal a√2 (a - length of edge).
ΔBFG has sides a, a√2 and a√3.
From Inverse Pythagorean Theorem:
a² + (a√2)² = (a√3)²
a² + 2a² = 3a²
3a² = 3a² CORRECT :)
ΔCDG and ΔEFG have sides a, a and a√2.
From Inverse Pythagorean Theorem:
a² + a² = (a√2)²
2a² = 2a² CORRECT :)