请教一道计量经济学的题

x'y=x'xβ+x'u
两边取期望E(x'y)=E(x'x)β+E(x'u)
由于假定x与u独立所以E(x'u)=E(E(x'u|x))=E(x'E(u|x))=0
有E(x'y)=E(x'x)β
得β=E(x'y)/E(x'x)
整理得
β=(x'y)/(x'x)
带入样本可得估计量b=(x'y)/(x'x)