If you see a letter included in a mathematical equation, you are looking at what is referred to as a "variable." Variables are letters that are used to represent varying numerical amounts. Variables can be negative or positive in nature. Learn to manipulate variables in a variety of ways if you take a high school or college algebra or calculus course. Follow certain rules if you are multiplying a positive and a negative variable.
Write out the multiplication sentence and leave a space where you will write the product.
Write both of the variables in the product if the variables are different. If the variables are the same letters, write that variable once in the product. For example, x * y would be xy, and x * x would be x in the first step of writing the product.
Add a negative sign to the answer. A negative variable times a positive variable will produce a negative product. For example, -x * y = -xy.
Add an exponent of 2 if the variable is the same. For instance, x * -x = -x^2.