JEE Math Practice Question

If $$A = \left[ {\begin{matrix} {\cos \theta } & {i\sin \theta } \\ {i\sin \theta } & {\cos \theta } \\ \end{matrix} } \right]$$, $$\left( {\theta = {\pi \over {24}}} \right)$$ and $${A^5} = \left[ {\begin{matrix} a & b \\ c & d \\ \end{matrix} } \right]$$, where $$i = \sqrt { - 1} $$ then which one of the following is not true?

1. A.$$a$$2 - $$c$$2 = 1
2. B.$$0 \le {a^2} + {b^2} \le 1$$
3. C.$$ a$$2 - $$d$$2 = 0
4. D.$${a^2} - {b^2} = {1 \over 2}$$