Q:

Finding voltages in a circuit with current source

I am trying to understand the basics of current source, but I don't know how to calculate the voltages v1 and v2. I tried to sketch the expression for current divider, but I think I didn't actually understood how to use it properly on an exercise.

simulate this circuit – Schematic created using CircuitLab

A:

You can calculate the current through the R2/R3/R4 branch using the current divider rule. Knowing the equivalent resistance of the R2/R3/R4 combination is 50 ohms,
$$I_{234} = I_1\frac{1/50}{1/50 + 1/75}$$
$$I_{234} = (25)\frac{75}{75 + 50}$$
$$I_{234} = (25)\frac{75}{125}$$
Which is the form given by your book.

