2 ρ l + R = 2 (2 ρ (l - x) + \frac{R_{l} (2 ρ x + R)}{R_{l} + 2 ρ x + R)}

${2\rho l + R = 2(2\rho (l - x) + \frac{R_l(2\rho x + R)}{R_l + 2\rho x + R)}}$

Error