Ratio of the three approximations considered in this paper to the exact calculation of the redshift space matter power spectrum multipoles, computed with the TNS prescription, for two f(R) models: |f_R0| = 10⁻⁵ and σ_v = 5.8 h⁻¹ Mpc (left panels), and |f_R0| = 10⁻⁶ and σ_v = 5.6 h⁻¹ Mpc (right panels), at redshift z = 1. The top, middle and bottom panels show the USA, the USA and EdS, and the ΛCDM-scr approximations, respectively. Blue and beige bands indicate errors on the monopole and quadrupole assuming a ΛCDM Gaussian covariance with V = 8.8 h⁻³ Gpc³ and no shot noise contribution. We note that the hexadecapole error fills the plot and so we have omitted it.