Seperable differential equations question

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SUMMARY

The discussion focuses on solving the separable differential equation dy/dx = 3x²(1+y²)^(3/2). The user has made significant progress by integrating both sides and substituting y = tan(u) to simplify the left-hand side. The integration leads to the equation sin(tan⁻¹(y)) = x³ + C. The user seeks assistance in simplifying the left-hand side further, specifically in finding sin(a) using a right triangle approach.

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Homework Statement


Solve the differential equation dy/dx = 3x2(1+y2)3/2


Homework Equations





The Attempt at a Solution


So far this is what I have (I'm almost finished) -

∫dy/(1+y)3/2 = ∫3x2 dx
Let y = tan(u) , dy = sec2(u)
Then (1+y2)3/2 = (tan2(u)+1)3/2 = sec3(u) and u = tan-1(y)
∫cos(u)du = ∫3x2dx
sin(u)+c = x3+c
sin(tan-1(y)) = x3+C

One question here, how do I simplify the left-hand side? I seem to have forgotten. Thanks!
 
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Draw a right triangle with an angle 'a' that satisfies tan(a)=y. Work out the hypotenuse. Now find sin(a).
 
thank you!
 

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