会~cov(x,y) = E((x-Ex)(y-Ey))cov(t*x,y) = E((t*x-E(t*x))(y-Ey)) = E((t*x-t*Ex)(y-Ey)) = t*E((x-Ex)(y-Ey)) = t*cov(x,y)不受影响的是相关系数corr(x,y)
