Simple Differential Equation: Finding General Solution for y'\cos(x) = \sin(2x)

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SUMMARY

The discussion centers on solving the differential equation y'cos(x) = sin(2x) and finding its general solution. The user initially attempted to isolate y' by rewriting the equation as y' = sin(2x)/cos(x) and integrating both sides. However, the correct solution involves recognizing the trigonometric identity sin(2x) = 2sin(x)cos(x), leading to the general solution y = -2cos(x) + C, where C is the constant of integration.

PREREQUISITES
  • Understanding of differential equations and their solutions
  • Familiarity with trigonometric identities, specifically sin(2x) = 2sin(x)cos(x)
  • Knowledge of integration techniques for trigonometric functions
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study integration techniques for trigonometric functions
  • Review trigonometric identities and their applications in calculus
  • Practice solving first-order differential equations
  • Explore the method of integrating factors for differential equations
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Students and educators in mathematics, particularly those focusing on calculus and differential equations, as well as anyone looking to strengthen their understanding of trigonometric identities and integration methods.

FeDeX_LaTeX
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Hello;

Found an exercise on simple differential equations on some website, got all correct except for this one. It only supplies answers but no method, but am stuck as to how they got their answer. Asked to find a general solution to the following differential equation:

y'\cos(x) = \sin(2x)

Here's my method:

Had to make it in the form y' = f(x), so;

y' = \frac{\sin(2x)}{\cos(x)}

Integrating both sides gives us;

y = \int \frac{\sin(2x)}{\cos(x)}dx

EDIT: Forget about method I wrote underneath. I saw my error. But can anyone show me how/why the above equates to -2cos(x) + C?

Thanks.
 
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Hello FeDeX_LaTeX! :smile:

You really need to learn your trigonometric identities …

in this case, sin2x = 2sinxcosx :wink:
 
Ack! I completely missed that! I knew that identity and it just completely fell out of my head... haha. Thanks! :)
 
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