MR. Organic Chemistry Tutor, thank you for another long video/lecture on Circles in Plane/Solid Geometry. The examples/problems are a solid blueprint for understanding Geometry, however there can be confusion on how to solve similar problems. Geometry has a variety of different problems in its library.
At 4:45 I thought you might have ended up with a 3,6,9 triangle but you calculated the hypotenuse as half as the diameter aka the radius. If it were a 3,6,9 triangle then the real measurement of the longer line is 18 units.
49:44 how do i know whether the 12 or the 20 should be negative/positive? You chose (x=-20 ), 20 to be negative -12*20 = 240 but isnt 12*(-20) also =240?