Arc length of vector function - the integral seems impossible

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The discussion revolves around calculating the arc length of the vector function v(x) = (e^x cos(2x), e^x sin(2x), e^x) using the arc-length formula S = ∫_a^b ||v(x)|| dx. The user struggles with the resulting integral, which appears overly complex and unmanageable. They express uncertainty about their approach, suggesting they might be missing a simpler method to solve the problem. The integral they present involves a complicated expression that includes trigonometric functions and exponential terms. Assistance is sought for tips on simplifying the integral or alternative methods to tackle the arc length calculation.
overpen57mm
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Homework Statement
Find the arc length from 0-3pi for v(x)=(e^x cos(2x), e^x sin(2x), e^x)
Relevant Equations
Arc length formula for vector equations
The vector equation is ## v(x)=(e^x cos(2x), e^x sin(2x), e^x) ##

I know the arc-length formula is ## S=\int_a^b \|v(x)\| \,dx ##

I found the derivative from a previous question dealing with this same function, but the when I plug it into the arc-length function I get an integral that I've tried and tried but just can't get anywhere with. The complexity of the problem also makes me think that I might be approaching it from the wrong direction. Here is the integral as I understand it: $$ \int{\sqrt{ (e^{2x}) ( (-2\sin(2x) + \cos(2x))^2 + (2\cos(2x)+\sin(2x))^2 + 1 ) }} \, dx $$

I would appreciate any tips on the integral or the problem as a whole, if there's another way to solve it that I haven't seen.
 
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You have an integral over ##\|(e^x \cdot F(x))'\|=\|e^x(F'(x)+F(x))\|=2e^x \sqrt{(\cos 2x -\sin 2x)^2+(\sin 2x+\cos 2x)^2+1^2}## where ##F(x)=(\cos 2x,\sin 2x,1).##
 
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fresh_42 said:
You have an integral over ##\|(e^x \cdot F(x))'\|=\|e^x(F'(x)+F(x))\|=2e^x \sqrt{(\cos 2x -\sin 2x)^2+(\sin 2x+\cos 2x)^2+1^2}## where ##F(x)=(\cos 2x,\sin 2x,1).##
Thanks, I guess I was blinded by the derivative I got from the previous question.
 
First, I tried to show that ##f_n## converges uniformly on ##[0,2\pi]##, which is true since ##f_n \rightarrow 0## for ##n \rightarrow \infty## and ##\sigma_n=\mathrm{sup}\left| \frac{\sin\left(\frac{n^2}{n+\frac 15}x\right)}{n^{x^2-3x+3}} \right| \leq \frac{1}{|n^{x^2-3x+3}|} \leq \frac{1}{n^{\frac 34}}\rightarrow 0##. I can't use neither Leibnitz's test nor Abel's test. For Dirichlet's test I would need to show, that ##\sin\left(\frac{n^2}{n+\frac 15}x \right)## has partialy bounded sums...