Q47 is a standard property of determinants and the proof is a bit long, if not tedious.
For Q48, if $ $Q$ $ is an $ $n\times{n}$ $ orthogonal matrix, then $ $Q^TQ=I_{n}$ $ . Take the determinant of both sides and use the result of Q47 to show that $ $\det{Q}=\pm{1}$ $ .
Hope it helps :)