C3 help :)

There are a lot you need to know

Differentiating ->

sinx -> cos x
cosx -> -sinx
tanx -> sec^2x
cosecx -> -cosecxcotx
secx -> secxtanx
cotx -> -cosec^2x

Its a good idea to memorise them all ! Helps doing these questions much faster

(edited 9 years ago)

Reply 5

Krollo

17

Original post by Super199

Right I got dy/dx= cot(x)

Are you just supposed to know the dy/dx of sin(x)=cos(x)?
Is there any other one's to know?

In terms of trig, you need to know the derivatives of sin(x) and cos(x). Everything else, like tan(x), can be deduced using those plus trig identities and the normal differentiation rules.

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Reply 6

Super199

OP

20

Original post by Dalilsp

There are a lot you need to know

Differentiating ->

sinx -> cos x
cosx -> -sinx
tanx -> sec^2x
cosecx -> cosecxcotx
secx -> secxtanx
cotx -> cosec^2x

Its a good idea to memorise them all ! Helps doing these questions much faster

Original post by Krollo

In terms of trig, you need to know the derivatives of sin(x) and cos(x). Everything else, like tan(x), can be deduced using those plus trig identities and the normal differentiation rules.

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Is there a video you can link me to explaining these? Thanks for the help :smile:

Reply 7

Vixanate

Original post by Arithmeticae

yes

d/dx cos(x) = -sin(x)

most of the rest can be derived from these

btw it's a bad habit to write stuff like 'what is the dy/dx of cos(x)' because there's no y involved

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It's perfectly normal to, stop spreading incorrect methods...

Reply 8

This is a video talking about differentiating specifically trig functions.. and this is a link to a long series of videos in which you can learn the entire Core maths syllabus from youtube :smile:

For C3, just keep scrolling down!

Hope this helped!

Reply 9

Original post by Krollo

In terms of trig, you need to know the derivatives of sin(x) and cos(x). Everything else, like tan(x), can be deduced using those plus trig identities and the normal differentiation rules.

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Nobody wants to be "deducing" simple trig functions in an exam. They should be instinctive.

Reply 10

Original post by Vixanate

It's perfectly normal to, stop spreading incorrect methods...

I would disagree.. Unless the equation being differentiated is y = cos (x), its fine to use dy/dx.. but however when just talking about the derivate of a trig function not being used in an equation, you would write d/dx(cos(x)) because there is no "y". Depends on the question and the way the answer is written out.

Reply 11

Original post by Vixanate

It's perfectly normal to, stop spreading incorrect methods...

No it's not. It is very sloppy notation.

Original post by Dalilsp

There are a lot you need to know

Differentiating ->

sinx -> cos x
cosx -> -sinx
tanx -> sec^2x
cosecx -> cosecxcotx
secx -> secxtanx
cotx -> cosec^2x

Its a good idea to memorise them all ! Helps doing these questions much faster

Not a big fan of the formula book then?

Reply 13

callum.30

1

Original post by Vixanate

It's perfectly normal to, stop spreading incorrect methods...

It's only true if y = cosx, the easiest way is to simply write an apostrophe next to the function e.g (cosx)'

Reply 14

Original post by Super199

Is there a video you can link me to explaining these? Thanks for the help :smile:

Did you take any notes at all ?

Reply 15

Original post by Mr M

Not a big fan of the formula book then?

Absolutely not. Dependance on the formula book is a big no no.. You should know what you are doing without any help at this stage - or if you will study maths further than A-level.

Reply 16