# Question: consider a single crystal of hexagonal symmetry since rotation by...

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Consider a single crystal of hexagonal symmetry. Since rotation by 60° about the z axis below (also known as the c-axis) must obviously leave the elastic constants unchanged, it can be shown that (i) C11 - C12 = 2 C66 . However, it can also be shown using relation (i) that (ii) C1’1’1’1’ = C1111 no matter what value θ assumes. Show that this latter statement is true by performing a transformation about the z axis with (i) taken into account.