In this video we'll learn how to use CPCTC (congruent parts of congruent triangles are congruent) as part of a proof. If you can establish that two triangles are congruent, then you can say that corresponding parts of the triangles are congruent.

In this video we'll learn about the isosceles triangle theorem, which tells us that, when we have an isosceles triangle (a triangle in which two of the sides are congruent), the angles opposite the congruent sides will also be congruent.

In this video we'll learn how to say whether or not two triangles are congruent, using the angle-angle-side (AAS) and hypotenuse-leg (HL) theorems of triangle congruence.

In this video we'll learn how to say whether or not two triangles are congruent, using the side-side side (SSS), angle-side-angle (ASA) and side-angle-side (SAS) theorems of triangle congruence.

In this video we'll learn how to determine whether two line segments are parallel, perpendicular, or neither. If they're parallel, they'll have the same slope. If they're perpendicular, their slopes will be the negative reciprocals of one another. If neither of these is the case, then the line segments are neither parallel nor perpendicular.

In this video we'll learn how to find the slope and midpoint of a line segment, given its endpoints. To find the slope, we'll use rise over run. To find the midpoint, we'll take the average of the x-values in the endpoints, and the average of the y-values in the endpoints, and these new values will define the midpoint.

In this video we'll learn how to use the midsegment of a trapezoid to establish a relationship between the smaller, interior trapezoid, and the larger, exterior trapezoid. When a line segment has its endpoints on the non-parallel sides of the trapezoid, and it's parallel to the parallel sides of the trapezoid (the bases), we can set up a proportion between the side lengths.

In this video we'll learn how to use the midsegment of a triangle to establish a relationship between the smaller, interior triangle, and the larger, exterior triangle. When a line segment has its endpoints on opposite sides of the triangle, and it's parallel to the base of the triangle, we can set up a proportion between the side lengths.

In this video we'll learn how to find the measures of the exterior angles of a polygon.

In this video we'll learn how to find the interior angle measures of polygons, no matter how many sides the polygon has.