Ncert Exercises & Solutions

23. A function f( $θ$ ) is defined as $f (θ) = 1 - θ + \frac{θ^{2}}{2!} - \frac{θ^{3}}{3!} + \frac{θ^{4}}{4!} + . . .$
Why is it necessary for f( $θ$ ) to be a dimensionless quantity?