## henpen 2 years ago $y^2=2px$ $\Rightarrow 2ydy=2pdx$ How is this achieved at? I've always gone with calculating $2y\frac{dy}{dx}=2p$ and multiplying both sides by dx. But I know that's heresy. What's the official story as to how it's arrived at?

1. henpen

I've always found it odd how it seems plucked out of thin air

here is a link this is called differentials chew on it

3. henpen

Oh differentials- I wasn't thinking!