Circ Basin

Failed to parse (syntax error): {\displaystyle \eta = \left{ \begin{array}{cc} \frac{W x_1 x_2}{2ghR} & f_c=0 \\ \frac{W f_c}{Rgh\kappa} \left[ \frac{R^2}{8} + \frac{1}{4}\left(\frac{2\kappa x_1 x_2}{f_c}-x_1^2-x_2^2\right) \right] & f_c \neq 0 \right. | }

(3)