How to define an altitude and draw them on acute, right, and obtuse triangles.
How to relate corresponding altitudes, medians and angle bisectors in similar triangles.
How to derive the area of a triangle formula using the rectangle area formula.
How to construct the orthocenter of a triangle.
The definition of climate.
How to identify a segment from the vertex angle in an isosceles triangle to the opposite side.
How to determine if two triangles in a circle are similar and how to prove that three similar triangles exist in a right triangle with an altitude.
How to define point of concurrency; how to identify the four main points of concurrency in triangles.