Are there any other areas of maths being taught wrong on this sort of scale? An online video course could be some scale. I once saw a video lesson on the Pyth

Are there any other areas of maths being taught wrong on this sort of scale? An online video course could be some scale. I once saw a video lesson on the Pythagorean theorem: Drawing a right-angled triangle, marking the hypothenuse with the letter h, marking both of the catheti with the letter c, then proceeds to write the formula h^2 = c^2 + c^2