doubt

Question

is there any other approach other than finding an inverse of P and multiplying with D

Comments

Rule -> if A=PDP' Then A is diagonal Matrix similar to D, where D is created with eigen values of A
Here given A=P'DP
Left multiply with P, we get => PA=DP
Right Multiply with P' on both sides
D=PAP' From the rule we can say D is Diagonal and is similar to A, from given options (i) and (ii) are the only diagonal matrices