$$U_{757}(x, y) = \frac{\left(1 - y\right)^{2} \left(1 - \sqrt{- \frac{4 x}{1 - y} + 1}\right)^{3}}{8 x^{3}}$$

$$T_{757}(n, m, k) = \frac{3 k {\binom{3 k + 2 n}{n}} {\binom{k + m + n - 1}{m}}}{3 k + 2 n}$$