resistance connected in series

When we connect the resistances in series , we must know that the current is constant when we move at the same line , and the voltage will be change when we move from resistance to another , and every resistance have voltage different values , from the previous we can write this equation :

I1 = I2 = Ieq

Vab = V1 + V2

Ieq * Req = Ieq * R1 + Ieq * R2

Now we can write the equation without Ieq as this :

Req = R1 + R2

From the equation we can get the value of Req