Official solution
Given,
sin\[\theta \] - cos\[\theta \] = \[\sqrt 2 \]cos\[\theta \]
\[ \Rightarrow \] sin\[\theta \] = \[\left( {\sqrt 2 + 1} \right)\]cos\[\theta \]
\[ \Rightarrow \] sin\[\theta \] = \[{{2 - 1} \over {\sqrt 2 - 1}}\]cos\[\theta \]
\[ \Rightarrow \] \[\left( {\sqrt 2 - 1} \right)\]sin\[\theta \] = cos\[\theta \] . . . (1)
This is for set P.
sin\[\theta \] + cos\[\theta \] = \[{\sqrt 2 }\]sin\[\theta \]
\[ \Rightarrow \] cos\[\theta \] = \[\left( {\sqrt 2 - 1} \right)\]sin\[\theta \] . . . .(2)
This is from set Q.
So, P = Q