coconut64
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Hi, for this question which is from the 2015 june C4 paper I don't get why the answer can't be in terms of degrees in the last part of the question to find t. Surely it makes more sense that t=27 years rather than 0.473( in radians). The mark scheme says specifically that only 0.473 is accepted but the question does not state this.

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf Question 7c
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Zacken
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(Original post by coconut64)
Hi, for this question which is from the 2015 june C4 paper I don't get why the answer can't be in terms of degrees in the last part of the question to find t. Surely it makes more sense that t=27 years rather than 0.473( in radians). The mark scheme says specifically that only 0.473 is accepted but the question does not state this.

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf Question 7c
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Surely you can see how unrealistic 27 years is?

Anywho, the reason you have to use radians is that all your derivatives and integrals depended on the fact that t was is radians. d/dt(sin t) = cos t only if t is in radians, if t is in degrees then that's not true anymore. So you solved your differential equation using things like integral of cos t = sin t, etc... which all made use of the fact that t was in radians.

So now you can't suddenly go back and use t as degrees, since the solution you have is one that depends on t in radians.

A lesson to learn here is that radians are infinitely better in most respects to degrees in calculus. So in an A-Level paper if you come across trigonometry in a calculus setting, it is 100% going to be in radians.
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ghostwalker
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(Original post by coconut64)
Hi, for this question which is from the 2015 june C4 paper I don't get why the answer can't be in terms of degrees in the last part of the question to find t. Surely it makes more sense that t=27 years rather than 0.473( in radians). The mark scheme says specifically that only 0.473 is accepted but the question does not state this.

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf Question 7c
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In any calculus of trig, (differentiation, integration, differential equations, etc.) the argument for the trig function is always in radians.
d(cos(x))/dx = - sin(x), etc. is only true when x is in radrians.
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_gcx
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(Original post by coconut64)
Hi, for this question which is from the 2015 june C4 paper I don't get why the answer can't be in terms of degrees in the last part of the question to find t. Surely it makes more sense that t=27 years rather than 0.473( in radians). The mark scheme says specifically that only 0.473 is accepted but the question does not state this.

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf Question 7c
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The integration identities that you have assumedly used are dependent on t being measured in radians.
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coconut64
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That makes sense, thanks for all the help
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