 This video is called Area of a Parallelogram and Area of a Square Formulas. These are two formulas that you are definitely going to have to know and be comfortable with and be able to use easily. The nice thing is, is that the formulas are quite simple. They're ones you've seen before. So hopefully with just a little review, you'll be able to remember these very quickly. Okay, let's start with Area of a Parallelogram. If you look at a parallelogram, remember, a parallelogram is a quadrilateral. It has four sides where both pairs of opposite sides are congruent. And it seems kind of weird to find the area of this shape because oftentimes parallelograms look kind of, for lack of a better word, tilty. But I'm going to ask you to imagine something. Notice I have a vertical red line, kind of an imaginary line cutting down through my parallelogram. Look at this red triangle that kind of, that was made when I cut down that imaginary line. I'm going to slide that part. So pretend this is a piece of paper and I'm cutting this triangle off. And I'm going to tape it back on right over here. It's not letting me get perfect, but it's pretty close. So you can see that this part of my parallelogram is gone because I taped it to the right hand side. So what shape is left a rectangle? So you're going to use the same formula to find area of a rectangle as you would to find area of a parallelogram. So to find the area of a rectangle, you just do base times height. And that's the formula that you're going to use for area of a parallelogram. But what is very important is that you pick the right base, you pick the right height. The base and the height must be perpendicular to each other. So let's go back to the picture and figure out what our base is, what our height is. So I'm going to erase kind of all that fancy work I did. Let's put the red triangle back where it started so we look more like a classic parallelogram. The base will most often times be along the bottom. It will be the whole side along the bottom. And then when you pick the height, you have to remember that the base and the height have to be perpendicular. So when it makes sense to choose the tilting line as your height because the tilting line in the base do not meet at 90 degrees. It's actually this imaginary line that you dropped down to make that triangle. That's what makes 90 degrees with the base, what's perpendicular. So that's going to be used as the height. If you wanted to drop down an imaginary line outside of the shape, that would be okay too because the base and that imaginary line meet at 90 degrees. So you could either have your height be in the shape or outside of the shape as long as it makes 90 degrees with your base. It meets it at 90 degrees. They're perpendicular. Alright, so that's one formula done. It doesn't get much simpler than that. As long as you remember that the base and the height have to be perpendicular. Area of a square. Well, squares, the key thing about squares is all four sides are the same. You're used to the idea of a square being just like a rectangle or a parallelogram now base times height where you would put the base at the bottom, the height on the side. But let's refine that a little bit. Let's make it a little more specific to squares. Since squares are all the same, the sides are all the same, we don't have to distinguish between a base and a height. We could simply call all four sides the same thing. You could call all four of them B's for bases, H for heights. I'm calling them S's to stand for sides because all the side lengths are the same. So in my formula, I replaced a B with an S. I replaced the H with an S. So you could say the area of a square is side times side. Let's make that even better and say it's the side length squared. So that's really nice because it reminds you that for area of a square all you really need is one side and you've got it since all four sides are the same. Remember when you do these problems, when you're finding area of a parallelogram and a square, you'll label your answers with units squared.