  We develop a new methodology called double-probe analysis with the aim of
minimizing informative priors in the estimation of cosmological parameters. We
extract the dark-energy-model-independent cosmological constraints from the
joint data sets of Baryon Oscillation Spectroscopic Survey (BOSS) galaxy sample
and Planck cosmic microwave background (CMB) measurement. We measure the mean
values and covariance matrix of $\{R$, $l_a$, $\Omega_b h^2$, $n_s$,
$log(A_s)$, $\Omega_k$, $H(z)$, $D_A(z)$, $f(z)\sigma_8(z)\}$, which give an
efficient summary of Planck data and 2-point statistics from BOSS galaxy
sample, where $R=\sqrt{\Omega_m H_0^2}\,r(z_*)$, and $l_a=\pi r(z_*)/r_s(z_*)$,
$z_*$ is the redshift at the last scattering surface, and $r(z_*)$ and
$r_s(z_*)$ denote our comoving distance to $z_*$ and sound horizon at $z_*$
respectively. The advantage of this method is that we do not need to put
informative priors on the cosmological parameters that galaxy clustering is not
able to constrain well, i.e. $\Omega_b h^2$ and $n_s$. Using our double-probe
results, we obtain $\Omega_m=0.304\pm0.009$, $H_0=68.2\pm0.7$, and
$\sigma_8=0.806\pm0.014$ assuming $\Lambda$CDM; and $\Omega_k=0.002\pm0.003$
and $w=-1.00\pm0.07$ assuming o$w$CDM. The results show no tension with the
flat $\Lambda$CDM cosmological paradigm. By comparing with the full-likelihood
analyses with fixed dark energy models, we demonstrate that the double-probe
method provides robust cosmological parameter constraints which can be
conveniently used to study dark energy models. We extend our study to measure
the sum of neutrino mass and obtain $\Sigma m_\nu<0.10/0.22$ (68\%/95\%)
assuming $\Lambda$CDM and $\Sigma m_\nu<0.26/0.52$ (68\%/95\%) assuming $w$CDM.
This paper is part of a set that analyses the final galaxy clustering dataset
from BOSS.
