请教关于相关系数和协方差的问题

我最近一直不懂怎么求这个公式 是关于根据协方差求相关系数的公式 网上也没有找到
所以开了此悬赏贴请教各位 此公式关于投资组合 貌似也是概率论和统计的公式  谢谢了 新年快乐！！！


公式在下面附件  D表示debt E表示equity

rD and rE can be considered as two random variables. Corr(rD, rE) is the correlation coefficient between these two variables. Cov(rD, rE) is the covariance between the two variables. sigmaD and sigmaE are the standard errors for rD and rE respectively.
Hope this is helpful.
Happy Chinese New Year!

hello thank u for replying my topic, virtually, i know what u r saying about! I just want to know the procedure how to prove these formula, could u tell me about this if u can! Happy new year!!! 2# jennyli1346

这是相关系数的定义：协方差/(A的标准差*B的标准差）