A rancher has a square cow pen with side length x. He decides to change the shape of the pen while still using the same amount of fencing materials. The equation (x+10)(x-10)=300 represents the relationship of the new side lengths (in feet) of the pen and its area (in square feet).
A: If 300 represents the area of the new cow pen, what do the expressions (x+10) and (x-10) each represent?