Dependence of the distance modulus on EOS of dark energy. Upper panel: distance modulus μ(z) for different values of the EOS parameters. The black line represents the standard flat ΛCDM model with Ω_m = 0.3, h = 0.7, w₀ = −1, w₁ = 0. The other curves correspond to different values of the CPL parameters w₀ and w₁. Bottom panel: z dependence of the percentage error in the distance modulus between the fiducial ΛCDM model and different flat CPL models, as in the left panel.