The Student Room Group
Reply 1
The dx was probably a mistake. The y (with the dot) implies dydt\frac{dy}{dt}

So it really should have been dy.

And yes, they did intergrate the RHS, but they simplified it. Try it yourself, and multiply by 6. You will get the correct anwser.
Reply 2
Hahaha, I was trying to find some magical way of integrating with respect to x......
Remember y(dot) = dy/dt

so the question is dy/dt = t^2/(y + e^y)

Separating variables (ie putting all of one variable on one side of the equation and treating the differential symbol as a fraction) and putting in the integral signs we get

Int (y + e^y ) dy = Int (t^2) dt

So (1/2)y^2 + e^y = (1/3)t^3 + c

Multiplying through by 3 gives

(3/2)y^2 + 3e^y = t^3 +c

Multiplying through by 2 gives:

3y^2 + 6e^y = 2t^3 + c

(I'm assuming here you understand the method of integration by separating variables, so I've just explain what you do in practice, rather than why we do it and why it works :smile:)
Reply 4
Roger Kirk
Remember y(dot) = dy/dt

so the question is dy/dt = t^2/(y + e^y)

Separating variables (ie putting all of one variable on one side of the equation and treating the differential symbol as a fraction) and putting in the integral signs we get

Int (y + e^y ) dy = Int (t^2) dt

So (1/2)y^2 + e^y = (1/3)t^3 + c

Multiplying through by 3 gives

(3/2)y^2 + 3e^y = t^3 +c

Multiplying through by 2 gives:

3y^2 + 6e^y = 2t^3 + c

(I'm assuming here you understand the method of integration by separating variables, so I've just explain what you do in practice, rather than why we do it and why it works :smile:)

Yeah I do, I just haven't slept and thus I was trying to integrate with respect to x, blindly following the question..... Thanks tho!!:biggrin:

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