In the function "y=x2-18x" the goal is to find the value of the letter x. We know that y equals x2-18x. First, recognize that x2 is the same thing as 2x. So changing the problem to "y=2x-18x". We can subtract 18x from 2x, which leaves us with -16x. Now the problem looks like this: y=-16x. In order to get x by itself, we will need to do the same thing to both sides of the equation. In this case, we want the answer to be x by itself, or (1x) which is the same thing. We divide both sides of the equation by (-16). We are left with the following: y/-16=x. Basically, in words, x equals y divided by negative 16.