In this video we'll learn how to find the circumference of a circle, which is the same as the perimeter of the circle. The only value we need to find the circumference is the length of the radius.

In this video we'll learn how to find the area of a circle, or areas of figures involving circles. If we know the radius of a circle, then we can find its area.

In this video we'll learn about the special properties of 30-60-90 triangles, which are triangles that have interior angle measures of 30 degrees, 60 degrees, and 90 degrees. With these kinds of triangles, there's always a special relationship between the side lengths.

In this video we'll learn about the special things that happen in the specific instance of a 45-45-90 triangle, which is a triangle whose three interior angles are 45 degrees, 45 degrees, and 90 degrees. This triangle, by definition, is an isosceles triangle, and it's one half of a square, split on the square's diagonal.

In this video we'll learn how to use pythagorean inequalities (inequalities derived from the pythagorean theorem) to say whether or not the triangle with the given side lengths is a right triangle, and acute triangle, or an obtuse triangle.

In this video we'll learn how to use the pythagorean theorem to find the lengths of the sides of a right triangle, and then add the side lengths together to find the perimeter of the triangle.

In this video we'll learn how to use the pythagorean theorem, which is a theorem that applies only to right-triangles (triangles that include a 90-degree angle). The pythagorean theorem tells us that the sum of the squares of the lengths of the legs is equal to the sum of the length of the hypotenuse (the longest side).

In this video we'll learn how to find the area of a triangle. Since a triangle is always half of a parallelogram, the area of the triangle can be found by multiplying the width by the height, and then dividing by 2.

In this video we'll learn how to find the area of a trapezoid, which is just a quadrilateral in which two of the opposite sides are parallel, and the other two opposite sides are not parallel. To find the area, we'll take the average length of the two parallel sides (the bases), and multiply by the height of the trapezoid.

In this video we'll learn how to find the area of a parallelogram, which is a quadrilateral (a four-sided figure), in which opposite sides are parallel. A rectangle is a parallelogram that has four 90-degree interior angles. Since the triangles on each end of the parallelogram can be moved to the same side, turning the parallelogram into a rectangle, we'll use the same formula to find the area of the parallelogram as we would to find the area of a rectangle.