We're looking at the stresses acting on a stress element. Here's our element and we're only going to be looking at stresses that occur on this face, this face, this face, and of course the one here on the back. This face right here is a free surface and so it doesn't come into any of our calculations. So what I want to do is to figure out what the stresses are on applying that cuts down through here like this. So what's that shear stress and what's that normal stress? And so we've got a defined angle here of theta. So now what do we do? Well, what we do is we need free biodegradable. So we're going to take a wedge here. We're going to cut that wedge out. And we're going to change it into a free biodegradable. So here's our wedge. And we have a normal insure stresses acting on all three planes. And if you will, we're given sigma x, sigma y, and tau xy, maybe I'm giving, maybe we've figured them out. And what our purpose is is to find these two stresses here. So I have to multiply the stresses times the areas that they are acting on. And those areas are different. For instance, the normal shear stress on this face here is acting on that area. Whereas the stresses that are acting here, the sigma x, for instance, is operating on that area. And they're definitely different. This one's smaller. And you can definitely see the difference when we talk about the third plane here. Where our sigma y is operating, that area is much less than that area. So our task will be, we'll draw free biodegradable, get those areas figured out and related. And then out of that will come stresses that occur on two separate planes.