Bunuel

Which of the following statements about the cube above must be true?
I. FD is parallel to GA.
II. ΔGCF and ΔAHD have the same area.
III. AF = GD
A. I only
B. I and II only
C. I and III only
D. II and III only
E. I, II, and III
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Quote:
Faces GHAB and FEDC are parallel to each other. We further also know that ∠GHA = ∠FED = 90° and GH=HA=FE=DE (sides of the same cube) which means that triangles GHA and FED are right angled isosceles triangles. Therefore, ∠HAG = ∠EDF = 45°
Therefore, we have two diagonals GA and FD which lie on parallel faces and have the same inclination of 45° with their base. Clearly, FD || GA
Quote:
II. ΔGCF and ΔAHD have the same area.
∠GFC = ∠HAD = 90° also GF=FC=HA=AD (sides of the same cube) therefore, both ΔGCF and ΔAHD are congruent to each other and will have the same areas.
Quote:
Both AF and GD are the body diagonals of the same cube and will be equal in length.
Hence, our answer is option E, all I, II and III are correct.