fitting_xdata = x[:21]
fitting_ydata = y[:21]
fit=polyfit(fitting_xdata,fitting_ydata,1,cov=True)
params=fit[0]
paramas_cov=fit[1]
m=params[0]
c=params[1]
fitted_y=m*fitting_xdata+c
plot(fitting_xdata,fitted_y,linestyle='-')
plot(fitting_xdata,fitting_ydata,marker='^',linestyle='')
xlabel('Concentration')
ylabel('Intensity')
show