I need to solve this separable differential equation
But what is ?
You want y to be the subject usually. ie: y = f(x).
Find C using the way Mr F said:
Once the value of C is known you can take the 4th root (obviously substitute in the value of C calculated in the previous step) :
As you said you cannot take the 4th root of a negative number so you will have domain restrictions in your answer since