Symmetric Equation from Two Points

If $x_2-x_1\ne 0$ If $y_2-y_1\ne 0$ If $z_2-z_1\ne 0$ For $P=(x_1,y_1,z_1)$, $Q=(x_2,y_2,z_2)$ $\frac{x-x_1}{x_2-x_1}=\frac{y-y_1}{y_2-y_1}=\frac{z-z_1}{z_2-z_1}$