Eric Nicholas K's answer to LockB's Junior College 1 H2 Maths Singapore question.

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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
1st
We continue to perform differentiation as usual using regular rules, but this time we do not attempt to make y the subject as we perform the differentiation.

Whenever you perform differentiation last year, in Sec 4,

y = x^2
dy/dx = 2x

What we are actually doing is
y = x^2
d/dx (y) = d/dx (x^2)

The process of writing dy/dx actually has this intermediary step of taking “d/dx” on both sides of the equation.

This is actually what happens for our question - we take d/dx on both sides, and whenever we see a “d/dx (y)”, it becomes dy/dx.
LockB
LockB
1 year ago
i dont really understand whats going on before the "now we....." tho

sorry for late reply i didnt get any notifications from the app
LockB
LockB
1 year ago
ohhh i get it now
also, when we differentiate 3y, do we write it as 3(dy/dx) or just dy/dx?
since d/dx(y) = dy/dx, but now theres a 3 infront and im not sure how to deal with it...

if uts d/dx(3x) its just 3 but i dont think d/dx(3y)=3
Eric Nicholas K
Eric Nicholas K
1 year ago
d/dx (3y)
= 3 times d/dx (y)
= 3 times dy/dx
= 3 dy/dx

dy/dx is in fact an expression for d/dx (y)

In general, whenever you do the differential of something which is y, we do everything the same as though it is an x, but we add an extra dy/dx behind as part of the chain rule

Eg

d/dx (10x^2) = 20x
d/dx (10y^2) = 20y times dy/dx

NOTE: d/dy (10y^2) = 20y without the dy/dx