I was studying number theory these days where Quadratic Gauss sum came up. https://en.wikipedia.org/wiki/Quadratic_Gauss_sum
My question was that:
What motivated them to construct Gauss Sum in the first place.
Why did they use $(\frac{t}{p})l^{at}$ rather than simply say $(\frac{t}{p})l^{t}$ in the first place.