rozzy
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hmm i'm a little confused when to change my calculator mode to radians when solving equations.

i know we have to change them whenever we see radians or pi, but how about when we see trig sin cos tan etc? and also exponential and log functions? because i'm doing this numerical method (iteration) question off C3 at the moment, and whenever i see exponential/log/trig being used, the answer is always when you use Radians in your calculator and not Deg.

I dont ever remember changing my calculator to radians mode when i had to work out trig before :confused: or is it just in iteration that we have to change it to radians?

thanks, hope someone can clear this up for me!
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GarethBrown
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I've been told to keep it in radians unless I'm told otherwise in the question. Degrees are stupid!
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iknowmole
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What sort of calculator do you have?
You only really need to change from radians to degrees or vice versa when an equation involves an angle, for example sine and cosine ect, i don't see why you would need to change for logs or exponentials. The question will normally state what you need to be in.
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iknowmole
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I have a casio fx-9750, on that you have to press shift, setup and then scroll down to the part that says either deg or rad and use the funtion buttons to change the mode. It is different for almost every calculator though.
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rozzy
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nope, this question has exponentials and cos in the same equation and does not state that i need to use radians. do u just have to use radians for numerical methods iteration or something?
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Sexy_fish
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yeah its very often diff
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iknowmole
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What is the question asking?
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GarethBrown
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C3 Numerical Methods question:

f(x)=5x-4sinx-2

This question then specifies that x is in radians though.

Which textbook are you using, the Heinneman one for Edexcel? I can't see a question in this which doesn't specify that x is in radians though!
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rozzy
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its a homework i've been given, i think its from an edexcel past paper.

the equation is f(x) e^x - 1 - cosx, and we have to show that 0.5 < a < 0.7

i know you just have to sub 0.5 and 0.7 in as X, but when i do it using the degree mode, the answer is wrong! but when i do it using the radian mode, the answer is right. also i did another question i found off the net with cosine in the iteration, and the answer was in radian mode too, and they didn't specify that x is in the radians mode either
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GarethBrown
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I think that at A-level it's in radians unless otherwise stated because radians is more useful than degrees.
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apple tree
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whatever they want, it's always worth checking your answer to make sure it makes sense (where possible), if necessary make a few approximations to check
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JeremyC
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(Original post by rozzy)
its a homework i've been given, i think its from an edexcel past paper.

the equation is f(x) e^x - 1 - cosx, and we have to show that 0.5 < a < 0.7

i know you just have to sub 0.5 and 0.7 in as X, but when i do it using the degree mode, the answer is wrong! but when i do it using the radian mode, the answer is right. also i did another question i found off the net with cosine in the iteration, and the answer was in radian mode too, and they didn't specify that x is in the radians mode either
Note that 0.5 and 0.7 don't have a degrees sign next to them - if there's no degrees sign, you should use radians.

Example
Suppose there's a question similar to the one you posted. Then, if you have to show:
\large 0.5^{\circ} &lt; a &lt; 0.7^{\circ} - use degrees.
\large 0.5 &lt; a &lt; 0.7 - use radians.
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Retakes
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When do you guys use radians on the calculator as apposed to degrees? As a rule should I keep it in radians mode? Whats am I meant to be using when ive got a questions with cot x sec x sec^" x or just cos x sin x or tanx?
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dlwilson97
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(Original post by Retakes)
When do you guys use radians on the calculator as apposed to degrees? As a rule should I keep it in radians mode? Whats am I meant to be using when ive got a questions with cot x sec x sec^" x or just cos x sin x or tanx?
There is ALWAYS something to look out for in the question so look for some of these:

- Obviously telling you to give your answer in degrees or radians
- The domain (0 < x < 2pi) for radians or (0 < theta < 360) for degrees (or other similar numbers)
- x normally means radians and theta normally means degrees, UNLESS IT SAYS OTHERWISE
- Any mention of pi in the trigonometry means radians
- Math error on your calculator? Check that you're in the right mode and if not, try the other one
- Look out for the degrees symbol ° anywhere

These are just a few examples so always double check if you're not sure. I've done over 50 A2 past papers and only ever seen one question that doesn't specify degrees or radians, and for that you ended up with actual values anyway so it didn't matter which you chose. Hope this helps and good luck tomorrow!
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