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# Good evening !

+5
694
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Good evening !

What would be the answer of : dx/dt * x2 = e2t
It would be great of you to answer !

Thks and happy new year

Dec 30, 2015

#3
+95360
+5

Thanks Guest,

I just want to play too.

$$\frac{dx}{dt} * x^ 2 = e^{2t}\\ x^2\frac{dx}{dt} = e^{2t}\\ \int x^2\frac{dx}{dt}\;dt = \int e^{2t}\;dt\\ \int x^2\;dx = \int e^{2t}\;dt\\ \frac{x^3}{3} = \frac{ e^{2t}}{2}+c_1\\ x^3 = \frac{ 3e^{2t}}{2}+c_2\\ x=\left [\frac{ 3e^{2t}+c_3}{2}\right]^{1/3}\\$$

Last line has been edited.

.
Jan 1, 2016
edited by Melody  Jan 1, 2016

#1
+10

Solve the separable equation x(t)^2 ( dx(t))/( dt) = e^(2 t):
Integrate both sides with respect to t:
integral ( dx(t))/( dt) x(t)^2 dt  =   integral e^(2 t)  dt
Evaluate the integrals:
x(t)^3/3  =  e^(2 t)/2+c_1
Solve for x(t):
x(t) = -((-3/2)^(1/3) (e^(2 t)+2 c_1)^(1/3)) or x(t) = (3/2)^(1/3) (e^(2 t)+2 c_1)^(1/3) or x(t) = (-1)^(2/3) (3/2)^(1/3) (e^(2 t)+2 c_1)^(1/3)
Simplify the arbitrary constants:
Answer: | x(t) = -((-3/2)^(1/3) (e^(2 t)+c_1)^(1/3))           or x(t) = (3/2)^(1/3) (e^(2 t)+c_1)^(1/3) or x(t) = (-1)^(2/3) (3/2)^(1/3) (e^(2 t)+c_1)^(1/3)

Dec 30, 2015
#2
+5

Oups I feel super dumb haha thanks !

Dec 30, 2015
#3
+95360
+5

Thanks Guest,

I just want to play too.

$$\frac{dx}{dt} * x^ 2 = e^{2t}\\ x^2\frac{dx}{dt} = e^{2t}\\ \int x^2\frac{dx}{dt}\;dt = \int e^{2t}\;dt\\ \int x^2\;dx = \int e^{2t}\;dt\\ \frac{x^3}{3} = \frac{ e^{2t}}{2}+c_1\\ x^3 = \frac{ 3e^{2t}}{2}+c_2\\ x=\left [\frac{ 3e^{2t}+c_3}{2}\right]^{1/3}\\$$

Last line has been edited.

Melody Jan 1, 2016
edited by Melody  Jan 1, 2016
#4
0

You might want to take another look at that last line Melody.

Bertie

Jan 1, 2016
#5
+95360
0

Thanks Bertie,

I think it is better now ?

Jan 1, 2016