f'(x) or dy/dx

[trendsetter123ftw]

Will you lose marks if a question states y = ... and you say f'(x)  = ... or if a question states f(x) = ...and you say dy/dx = ...?
Thanks

[Sine]

Will you lose marks if a question states y = ... and you say f'(x)  = ... or if a question states f(x) = ...and you say dy/dx = ...?
Thanks

It's definitely notationally incorrect so a good assessor would take marks off.

[trendsetter123ftw]

It's definitely notationally incorrect so a good assessor would take marks off.

So if there was a question f(x) = (5x+1)^7
and I let u = 5x+1, would i have to say u' = 5?
so then f(x) = u^7
so f'(x) = 7u^6
so then f'(x) = (7u^6)*(5) = 7(5x+1)^6(5) = 35(5x+1)^6
Is the above correct notation for f(x)?

[Sine]

So if there was a question f(x) = (5x+1)^7so then f(x) = u^7
so f'(x) = 7u^6
and I let u = 5x+1, would i have to say u' = 5?
so then f(x) = u^7
so f'(x) = 7u^6
so then f'(x) = (7u^6)*(5) = 7(5x+1)^6(5) = 35(5x+1)^6
Is the above correct notation for f(x)?

I think to remove any doubt if you want to switch up from f(x) to dy/dx just make sure to say let f(x) = y
because technically when you say

so then f(x) = u^7
so f'(x) = 7u^6

you are differentiating the LHS with respect to x and the RHS with respect to u which is mathematically incorrect.

Also you move from

so f'(x) = 7u^6
so then f'(x) = (7u^6)*(5) = 7(5x+1)^6(5) = 35(5x+1)^6

In the same question if you have two equations which don't agree you automatically lose a mark (if the assesor picks up on it)