What does II mean in math notation?

[Lorens]

Easy math problem ...

My question is just what do II means?

 

[andrevdh]

Me thinketh that it means that you get the total resistance by adding the two parallel branches of resistances. In the one branch are two resistors in series (R2,R3), in the other branch a single resistor (R4). It is your teacher's own private unconventional notation.

 

[nazzard]

This notation comes in handy if you have to deal with larger circuits and I've seen and used it myself before as well.

The total resistance R for two parallel resistors R1 and R2 can be written as:

$$R=(R_1 \parallel R_2)=\frac{R_1\,R_2}{R_1+R_2}$$

Regards,

nazzard