Factoring
Quickest when the quadratic splits over the integers. For 2x^2 - 5x - 3 = 0, look for two numbers multiplying to (2)(-3) = -6 and adding to -5: they are -6 and 1. Split the middle term into -6x + x, group into 2x(x - 3) + 1(x - 3), and factor out (x - 3)(2x + 1) = 0. The zero-product rule gives x = 3 and x = -1/2.