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How to solve is trigonometric differentiation problem?

https://postimg.cc/pmw3kyj5

The ans is D but Im confused on how to solve it, mainly due to the position of the cosine
Original post by MonoAno555
https://postimg.cc/pmw3kyj5

The ans is D but Im confused on how to solve it, mainly due to the position of the cosine


Post what you've tried as per forum rules
Original post by MonoAno555
https://postimg.cc/pmw3kyj5

The ans is D but Im confused on how to solve it, mainly due to the position of the cosine

Not sure what you mean by the position of the cosine, but the trig term is
cos(2pi/lambda(x-vt))
so acceleration is the usual second derivative wrt time. Then a bit of simple reasoning to get the maximum value.
(edited 1 year ago)
Original post by mqb2766
Not sure what you mean by the position of the cosine, but the trig term is
cos(2pi/lambda(x-vt))


Oh I understand it now because of the brackets you put!. it isn't written like that in the book so I thought it meant s(x,t) = 2pi/lambda(cos(x-vt)). i will try it again, thank you
Original post by mqb2766
Not sure what you mean by the position of the cosine, but the trig term is
cos(2pi/lambda(x-vt))
so acceleration is the usual second derivative wrt time. Then a bit of simple reasoning to get the maximum value.

That's exactly why I asked them to post what they'd done ...
Original post by MonoAno555
Oh I understand it now because of the brackets you put!. it isn't written like that in the book so I thought it meant s(x,t) = 2pi/lambda(cos(x-vt)). i will try it again, thank you


Thinking about the coefficient of t inside the cos term, the answer is fairly straightfoward.

While the argument may look a bit strange,the v/lambda = frequency (Hz) and the 2pi (and t) maps it to radians. So it does make sense. x-vt would not be in radians.
https://www.desmos.com/calculator/bjt6dleg5h
from
https://www.physicsforums.com/threads/what-exactly-does-x-vt-mean-in-the-wave-equation.836348/
is a decent picture to have inside your head.
(edited 1 year ago)

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