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# Maths question watch

1. Hi guys,why does the calculator have to be set to radians here for the first part of i)?

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2. (Original post by sienna2266)
Hi guys,why does the calculator have to be set to radians here for the first part of i)?

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At A level we assume radians unless we are told otherwise.
3. (Original post by Muttley79)
At A level we assume radians unless we are told otherwise.
Thanks so much! Also, I don't quite understand ii) - the when is the water rising most rapidly bit in particular.

Could you please help me with this?

Edit: Actually, I get it now .
4. (Original post by sienna2266)
Thanks so much! Also, I don't quite understand ii) - the when is the water rising most rapidly bit in particular.

Could you please help me with this?

Edit: Actually, I get it now .
Also d/dx (sin x) = cos x is only true in radians
5. (Original post by Muttley79)
Also d/dx (sin x) = cos x is only true in radians
Thanks so much for mentioning this. But what about the other derivatives e.g. d/dx (cosx) ... d/dx (tanx) and etc...?

I have attached an image from a doc which says that "that the derivative results rely on measuring x in radians " so does the radians thing apply to all types of trig derivatives and also all trig questions(unless specified to do it in degrees) ?

6. (Original post by sienna2266)
Thanks so much for mentioning this. But what about the other derivatives e.g. d/dx (cosx) ... d/dx (tanx) and etc...?

I have attached an image from a doc which says that "that the derivative results rely on measuring x in radians " so does the radians thing apply to all types of trig derivatives and also all trig questions(unless specified to do it in degrees) ?
Yes, all trig has to be in radians when calculus is involved [unless we want to add that constant to everything]. My post was just an example for the question you were doing.
7. (Original post by Muttley79)
Yes, all trig has to be in radians when calculus is involved [unless we want to add that constant to everything]. My post was just an example for the question you were doing.
Thanks so much, so when calculus is not involved in trig then you don't have to have the calculator in radians mode?
8. (Original post by sienna2266)
Thanks so much, so when calculus is not involved in trig then you don't have to have the calculator in radians mode?
It depends on the question - sometimes trig equations have to be solved in radians [the range will tell you which to work in] and also when you are finding areas of sectors we often work in radians. It should be clear from the question.
9. (Original post by Muttley79)
It depends on the question - sometimes trig equations have to be solved in radians [the range will tell you which to work in] and also when you are finding areas of sectors we often work in radians. It should be clear from the question.
Thank you very much But it is not clear in this question: They don't mention a specific range and also you are not using calculus in this trig so how do you know that the calculator must be set to radians here specifically? We are only finding the height of the water so why do we set the calculator to radians?

10. (Original post by sienna2266)
Thank you very much But it is not clear in this question: They don't mention a specific range and also you are not using calculus in this trig so how do you know that the calculator must be set to radians here specifically? We are only finding the height of the water so why do we set the calculator to radians?

We are going to differentiate and there's no degree symbol - a question wil be in degrees OR radians; here it must be radians.
11. (Original post by Muttley79)
We are going to differentiate and there's no degree symbol - a question wil be in degrees OR radians; here it must be radians.
Sorry to be so annoying. But what if the question ends just there (so there is no next part to the question and so we don't differentiate in the next part)... Since they don't tell you to work with degrees or radians, then do you just work with radians because we have got a trig here?
12. (Original post by sienna2266)
Sorry to be so annoying. But what if the question ends just there (so there is no next part to the question and so we don't differentiate in the next part)... Since they don't tell you to work with degrees or radians, then do you just work with radians because we have got a trig here?
t is measured in hours so 0.5t is going to be small [tides go up and down in hours not over several days - try working out some values and see what I mean] and, more importantly, there's no degree symbol in the equation.
13. (Original post by Muttley79)
t is measured in hours so 0.5t is going to be small [tides go up and down in hours not over several days - try working out some values and see what I mean] and, more importantly, there's no degree symbol in the equation.
Thanks
14. (Original post by sienna2266)
Sorry to be so annoying. But what if the question ends just there (so there is no next part to the question and so we don't differentiate in the next part)... Since they don't tell you to work with degrees or radians, then do you just work with radians because we have got a trig here?
I think an exam question would be clearer if it was just part i) so you don't need to worry.

But anyway repeating what was said above, just assume radians unless the question mentions degrees then you can't go wrong. If a question involves calculus then the trig functions will always have inputs measured in radians.
15. (Original post by Notnek)
I think an exam question would be clearer if it was just part i) so you don't need to worry.

But anyway repeating what was said above, just assume radians unless the question mentions degrees then you can't go wrong. If a question involves calculus then the trig functions will always have inputs measured in radians.
Thank you

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