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

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Discussion Overview

The discussion revolves around finding the general solution to the differential equation y'cos(x) = sin(2x). Participants explore methods of solving the equation and clarify trigonometric identities relevant to the problem.

Discussion Character

  • Homework-related, Technical explanation

Main Points Raised

  • One participant reformulates the equation to y' = sin(2x)/cos(x) and attempts to integrate it.
  • Another participant points out the need to apply trigonometric identities, specifically that sin(2x) can be expressed as 2sin(x)cos(x).
  • A later reply acknowledges the oversight regarding the trigonometric identity and expresses gratitude for the correction.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the solution method, as the discussion focuses on identifying errors and clarifying identities rather than establishing a definitive solution.

Contextual Notes

The discussion highlights a potential misunderstanding of trigonometric identities that may affect the integration process, but does not resolve the integration steps or the final solution.

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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