Differential Equation with an Initial condition

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The differential equation x(dy/dx) = 3y + x^4cos(x) with the initial condition y(2π) = 0 can be transformed into a standard first-order linear form by dividing both sides by x. This results in the equation dy/dx - (3/x)y = x^3cos(x). The discussion highlights challenges in separating variables and applying the Bernoulli method effectively. A hint suggests using integrating factors to solve the transformed equation. The solution approach emphasizes the importance of recognizing the equation's structure for effective resolution.
Zinggy
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Homework Statement


x(dy/dx) = 3y +x4cos(x), y(2pi)=0

Homework Equations


N/A

The Attempt at a Solution


I've tried a couple different ways to make this separable, but you always carry over a 1/dx or 1/dy term and I can never fully separate this. I've also tried to do a Bernoulli differential equation method by doing a change of variable and putting it in the form: xy'-3y = x4cos(x) but it's not quite the right format to allow that to work, I would need it to be y4cos(x) instead.
 
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Hint: Integrating factors.
 
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Zinggy said:

Homework Statement


x(dy/dx) = 3y +x4cos(x), y(2pi)=0

Homework Equations


N/A

The Attempt at a Solution


I've tried a couple different ways to make this separable, but you always carry over a 1/dx or 1/dy term and I can never fully separate this. I've also tried to do a Bernoulli differential equation method by doing a change of variable and putting it in the form: xy'-3y = x4cos(x) but it's not quite the right format to allow that to work, I would need it to be y4cos(x) instead.
Divide both sides of the DE by ##x##. That gives a very standard first-order DE with a well-known solution. (Hint: the hint from #2).
 
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Divide both sides by ##x## and rearrange into:
##\dot y -\frac 3 x y = x^3 cos(x)##
Since you are studying differential equations I trust that you can figure out how to solve this.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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