A triangular wave which goes from -12V to 12V is applied to the inverting input of the OP-AMP. Assume that the output of the OP-AMP swings from +15V to -15V. The voltage at the non-inverting input switches between.

If $${V_i} = {V_1}\,\,\sin \left( {\omega \tau + \phi } \right),$$ then the minimum and maximum values of $$\phi $$ (in radians) are respectively

The transfer function $${V_o}\left( s \right)/{V_i}\left( s \right)$$ is