@Sam that is essentially it, but there is an actual reason. Combining distributions doesn't work if you are adding standard div, so it's easier for it to be written as a variance.
Hey thanks so much for this highly useful video... 11:58 I got the part you said before... but I saw in every markscheme that they condone leaving answers in column notation if the question was asked in i / j form...
horizontal component of T acts left and that is the only force acting left and therefore there needs to be a frictional force acting right to counteract it(as friction only force moving right)
Why do we need a comparison? Both give up vast amounts of their time dedicated to helping students achieve the best they can, for FREE! No need to disrespect one or another, they both are amazing.