The solution can be determined if we can specify the value of the arbitrary constant Cā. We do this by using the initial condition. When x=0, y is equal to -18. Substitute this to the general solution.
y = 1/(1 + Cāeā»Ė£)
-18 = 1/(1 + Cāeā°)
-18 = 1/(1+Cā)
Cā = -1- 1/18 = -19/18
Therefore, the specific solution is:
y = 1/(1 - 19eā»Ė£/18)