$$\color{rgb(0,0,0)}x_A$$

$$\color{rgb(0,0,0)}x_B$$

$$\color{rgb(0,0,0)}y_A$$

$$\color{rgb(0,0,0)}y_B$$

$$\color{rgb(127,0,127)}x_B-x_A$$

$$\color{rgb(255,0,0)}y_B-y_A$$

$$\color{rgb(0,0,255)}\text{AB} = \sqrt{\left( x_B-x_A \right)^2+\left( y_B - y_A \right)^2}$$