I have a system of 3 equations, each equation has 3 variables, $x,y,z$ :
$$x + y = z \\ x_1 + y_1 = z_1 \\x_2 + y_2 = z_2$$
Is $(\frac{x}{x_1} \cdot x_2 )+ (\frac{y}{y_1} \cdot y_2) = (\frac{z}{z_1})\cdot z_2$ true if all the variables are decimal and positive numbers ?