(c) Given, $f(x) = \frac{ax + b}{cx + d}$ It reduces the constant function if $\ \ \ \ \ \ \ \ \ \ \frac{a}{c} = \frac{b}{d}\ \Rightarrow \ \ \ ad = bc$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.