-(R1*R3*R4*R7*x_2 + R1*R4*R6*R7*x_2 + R3*R4*R6*R7*x_2)/(R1*R2*R3*R4 + R1*R2*R3*R5 + R1*R2*R3*R7 + R1*R2*R4*R5 + R1*R2*R4*R6 + R1*R2*R4*R7 + R1*R2*R5*R6 + R1*R2*R6*R7 + R1*R3*R4*R7*x_1 + R1*R3*R4*R7 + R1*R3*R5*R7 + R1*R4*R5*R7 + R1*R4*R6*R7*x_1 + R1*R4*R6*R7 + R1*R5*R6*R7 + R2*R3*R4*R6 + R2*R3*R5*R6 + R2*R3*R6*R7 + R2*R4*R5*R6*x_1 - R2*R4*R5*R6*x_2 + R2*R4*R5*R6 + R2*R4*R6*R7*x_1 - R2*R4*R6*R7*x_2 + R2*R4*R6*R7 + R3*R4*R6*R7*x_1 + R3*R4*R6*R7 + R3*R5*R6*R7 + R4*R5*R6*R7*x_1 - R4*R5*R6*R7*x_2 + R4*R5*R6*R7)