There are 4 isosceles triangles: ABD, CDE, BCE, and AEC.
Δ ABD => 45° + 67.5° + 67.5° = 180°
Δ CDE => 45° + 67.5° + 67.5° = 180°
Δ BCE => 45° + 90° + 45° = 180°
Δ AEC => 45° + 67.5° + 67.5° = 180°
Triangle AEC is an isosceles triangle, because 2 of its 3 angles are equal, and as a result of that, 2 of its sides are equal as well.