$\int \frac{1}{x} dx$ is an unsolvable problem using standard laws of Calculus (power rule) without the use of the function $f(x) = \ln x$ which was handcrafted by mathematicians to solve such problems. If we go back even further, the function $f(x) = \sin x$ was also a transcendental function used to describe the changing relationship between the arc and chord of a circle - it was not until 1682 that Leibniz proved that $\sin x$ was indeed not expressible as an algebraic function. Today, we still have expressions that can't be evaluated precisely such as $\int x^x dx$ because it cannot really be expressed as a function using the standard toolkit of algebraic and transcendental functions that we currently have. This begs the question, when is it appropriate for mathematicians to come up with new transcendental functions as solutions to "unsolvable problems" including but certainly not limited to the integral expression presented above?