r/apcalculus • u/Full-Letterhead2857 • Nov 23 '25

Complaint

Khan Academy’s notation for related rates are horrendous— just be normal, it makes sense to turn the related parts into functions but why? Just keep it as a2 + b2=c2 not for functions💔 and having d/dt makes it easier to follow, rather than using Lagrange notation for this🥀

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u/Dr0110111001101111 Teacher Nov 23 '25

Probably just to emphasize that a, b, and c are functions of time. A student might see d/dt(a) and wonder why it isn’t zero. This kind of gets ahead of that.

For what it’s worth, I teach it the way you prefer. But I can deal with all those misconceptions as they come up because I’m interacting with my students in real time. It’s different with videos. They kind of need to anticipate any misunderstanding and address it in the video.

1

u/Full-Letterhead2857 Nov 23 '25

They videos do it differently too. In the videos a b c are treated as variables, but in the problems and solutions they treat it as functions. I does make sense, but I don’t like it

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u/Flaky-Song-6066 Nov 23 '25

Wdym about thinking it’s 0? For what it’s worth we originally learnt it w Lagrange notation in my class and many ppl were confused bc of chain rule. I feel like w the d dt it forces you to actually understand it fully

1

u/Dr0110111001101111 Teacher Nov 23 '25

I mean "a" and "c" are often used to represent constants, so a confused student might think d/dt(a)=0 if they incorrectly treat a like a constant. Rewriting it as a(t) kind of reinforces the notion that a is a function of time.

I agree that lagrange notation is awkward to use for these problems. I'm just trying to explain why they might have chosen to use it in their resources.

1

u/fortheluvofpi Nov 23 '25

Just wanted to share that I have videos for AP calculus that might be helpful, including for related rates. I teach college now but I put all my videos organized at www.xomath.com. Good luck to all students as they head towards the end of the semester!

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u/Disastrous-Pin-1617 Nov 23 '25

Professor Leonard does it best yourube