Power law inflation with a non-minimally coupled scalar field in light of Planck 2015 data: the exact versus slow roll results

We study the power law inflation in the context of non-minimally coupled to the scalar curvature. We analyze the inflationary solutions under an exact analysis and also in the slow roll approximations. In both solutions, we consider the recent data from Planck 2015 data to constraint the parameters in our model. In this framework, we find that in the slow roll approximations the spectral scalar index nS>1$n_{S} > 1$, during the power law inflation.