How Do You Solve the Differential Equation dx/dt = cos(x + t)?

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SUMMARY

The differential equation dx/dt = cos(x + t) can be solved using the substitution z = x + t, simplifying the equation to 1/(cos(z) + 1). The solution involves separating variables and integrating, leading to the integral of the form int(1/(cos(z) + 1)) = ln(t) + C. This method avoids the complications of expanding cos(x + t) and provides a clear path to the solution.

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  • Understanding of basic differential equations
  • Familiarity with trigonometric identities
  • Knowledge of integration techniques
  • Experience with variable substitution in calculus
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  • Study the method of separation of variables in differential equations
  • Learn about trigonometric integrals, specifically int(1/(cos(z) + 1))
  • Explore variable substitution techniques in solving differential equations
  • Review the properties of the cosine function and its applications in differential equations
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Homework Statement



solve the differential eqn: dx/dt=cos(x+t)

Homework Equations





The Attempt at a Solution



x'=cos(x+t)=cosxcost-sinxsint

let z=sinx, dz/dx=cosx

dz/dt=(dz/dx).(dx/dt)=cosx(dx/dt)

however this substitution quickly fails

any ideas?

thanksx
 
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Try something simpler. Hint: You don't need to expand cos(x+t).
 
Used z=x+t

get: int(1/(cosz+1)=in(t) on separation of the variables.

cheers
 
Can you finish the problem now?
 

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