问题如下：
The independent variable is the ratio of net income to sales for restaurants with a market cap of more than $100 million and the dependent variable is the ratio of cash flow from operations to sales for those restaurants.
What is the correlation between X and Y?
选项：
A.-0.7436.
B.0.7436.
C.0.8623.
解释：
C is correct.
For a regression with one independent variable, the correlation is the same as the Multiple R with the sign of the slope coefficient. Because the slope coefficient is positive, the correlation is 0.8623.
助教老师我这个问题和这个题目不是直接相关。
何老师讲过R^2代表拟合值Y^对于真实值Y的拟合程度；如果要求correlation, 只需要求出multiple R, 也就是root of R^2 （这里先没有考虑正负号）
到这里，R^2 可以理解为 （correlation)^2, 但是在拟合的过程中，R^2 的表达式并不能体现出( correlation)^2, 可以请助教老师帮我梳理一下逻辑么？这样我能够理解的更深刻。
