23. A function f(θ) is defined as f(θ)=1θ+θ22!θ33!+θ44!+ ...
Why is it necessary for f(θ) to be a dimensionless quantity?

Hint: Apply the principle of dimension homogeneity.

Since f(θ) is a sum of different powers of θ and it is a dimensionless quantity.

By the principle of dimension homogeneity, as RHS is dimensionless, hence LHS should also be dimensionless.