# For a perfect correlation between the variables $x$ and $y$ the line of regression is $ax+by+c=0$ where $a,b,c > 0$ then $r$ is

$\begin {array} {1 1} (A)\;0 & \quad (B)\;-1 \\ (C)\;1 & \quad (D)\;None \: of \: these \end {array}$

$ax+by+c=0$ has slope $-\large\frac{a}{b} <0$
So the two variables are in perfect negative correlation
Hence $r = -1$
Ans : (B)