Then use values that won't load the source too much or give an output impedance that will be loaded by what's connected to the output.
If the source and load impedances are significant then you should account for them in your calculations. If the load impedance is too low or varies significantly then you'll need a buffer amplifier.
If the value of both voltage-dividing resistors are unknown or you want to produce a voltage at the "take-off" point, you need to know the current to be delivered and the allowable voltage-drop. With these two values you can start to work out the values for the two voltage-dropper resistors.
Another question using a voltage divider circuit how would one work out the following ?
atm
Vin =9v
vout = 2v
R1 = 525 ohm
R2 150 ohm
a.I want to apply a load across R2 which requires 2v and 20 ma to function how do I compensate for the load on voltage drop and ensure that it has can draw 20 ma ?
b.When designing a voltage divider how can one be sure to get the desired output that uses resistors in a range that are available ?