Why does polyfit gives two outputs?

Hi, I want to plot a line passing through a set of points, which is as in the code below.   To determine the slope I used polyfit.   But it gives two outputs.   I wonder which output I should consider out of the two outputs it is giving me? clc; clear; phi_1 = [0.1724*pi 0.1472*pi 2.18*pi 2.25*pi 4*pi 3.588*pi 1.012*pi 4.112*pi 4.31*pi 4.25*pi 0.832*pi]; x1 = linspace(0,1,11); figure(1) plot(x1,phi_1,'o'); coefficients1=polyfit(x1,phi_1,1) slope1=coefficients1(1); coefficients1=polyfit(x1,phi_1,1) coefficients1 = 1×2 7.6641 3.8373 slope1=coefficients1(1);