Jake Burton
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 May 16 accepted Calculating permutations if the sequences have to be in ascending order? May 16 awarded Supporter May 16 asked Calculating permutations if the sequences have to be in ascending order? May 2 comment In integration notation - why can you multiply du by a number? Say then you have the function $f(x) = x^{2}$ for which $f'(x) = 2x$. So the equation of the tangent at $x = 1 e.g. f'(1)$ is 2 but how does that relate to $dy = f'(1)dx$? Oh I think I see it now $dy = 2 dx$ is a function just like $y=mx+c$ which you can manipulate? Is that correct? May 2 comment In integration notation - why can you multiply du by a number? So the derivative $f'(x)$ is a function that describes the gradient of a function $f(x)$ but for a given point $a$ it is also the equation/function of a tangent - I'm assuming thats roughly what is meant by linear approximation. But this tangent $f'(a)$ also takes a variable $dx$ which makes it describe $dy$, how does that work? May 2 awarded Scholar May 2 comment In integration notation - why can you multiply du by a number? Makes sense, thanks! May 2 accepted In integration notation - why can you multiply du by a number? May 2 comment In integration notation - why can you multiply du by a number? Out of interest because I haven't come across it yet, where else is $dx$ written on its own? May 2 comment In integration notation - why can you multiply du by a number? I think I understand, du & dx are 'made up' for want of a better term quantities that we use to manipulate. So $\int \sin(u)$ $2du$ is actually ($\int \sin(u)) * (2) * (du)?$ or rather $(\int \sin(u) du) * 2$ May 2 awarded Analytical May 2 awarded Student May 2 asked In integration notation - why can you multiply du by a number?