A theoretical issue from portfolio management: For a positive correlation (ranged from 0 to 1) between two assets (one low-risk and the other high-risk), there will be a negatively sloped portion in the minimum-variance frontier of that two assets if the correlation coefficient is smaller than the value we get from dividing the standard deviation of the low-risk asset by that of the other high-risk asset. Why? Someone, please help. p.s. I got the answer from a different perspective; however, I need to know why CFAI didn’t explain this from my perspective, rather than this one.