Solving a Trig Problem - is this iterative only?

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SUMMARY

The discussion focuses on solving the equation q(t) = e^{-20t} (5cos(40t) + \frac{5}{2}sin(40t)) to find when it equals zero for the first time. The key insight is that the equation simplifies to 5cos(40t) + \frac{5}{2}sin(40t) = 0, leading to the relationship cos(40t) = -\frac{1}{2}sin(40t). The solution involves transforming this into tan(40t) = -2 and applying the arctan function. Iterative methods, such as using Excel, are unnecessary as the problem can be solved analytically.

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Homework Statement



Find when this is "0" for the first time:

q(t) = e^{-20t} (5cos(40t) + \frac{5} {2} sin(40t))


Homework Equations





The Attempt at a Solution



0 = e^{-20t} (5cos(40t) + \frac{5} {2}sin(40t))

0 = (5cos(40t) + \frac{5} {2}sin(40t))

cos(40t) = -\frac{1} {2}sin(40t))


Is the best way to solve this perform interations?

Thanks
Sparky
 
Last edited:
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Iterations on what? You've basically solved it. Make that into tan(40t) = -2 and apply arctan. If you don't want a negative number in the argument, you can use the fact that arctan is an odd function.
 
Thanks Kreizhn,

I'm now embarrassed.

this was not seeing the forest for the trees.

I was about to open Excel and try different values of t until I got it to work out.

Thanks
Sparky
 

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