consider to model:Yi=βo+β1Xi+εi

Given some observed datay1,x1,y2,x2,...,yn,xn

Show that the estimated sample covariance Cov(εi,Xi) MUST equal 0 in an OLS regression, where εi=Yi+β0-β1Xi is the estimated residual from the model. In other words, show that the sample correlation between the estimated errors and theXvariable isalwaysequal to 0 in OLS regression.

thx for help!