\text { You are given that the matrix, } A=\left(\begin{array}{ccc} 1 & 0 & 0 \\ 0 & \frac{2 a-a^{2}}{3} & 0 \\ 0 & 0 & 1 \end{array}\right) \text

{ where } a \text { is a positive constant, } represents the transformation R which is a reflection in 3-D. a) State the plane of reflection of R. b) Determine the value of a. c) With reference to R explain why A? = 1, the 3x3 identity matrix.