In circuit analysis, three equivalent expressions of Ohm's law are used interchangeably. The interchangeability of the equation may be represented by a triangle, where V (voltage) is placed on the top section, the I (current) is placed to the left section, and the R (resistance) is placed to the right. The line that divides the left and right sections indicate multiplication, and the divider between the top and bottom sections indicates division (hence the division bar). Basically, cover up the letter that you want to solve for and the image will show the relationship necessary to solve for what you want:
