For the differential equation dy/dt=ky, k is a constant, y(0)=24, and y(1)=18. What is the value of k?

The equation is separable, so solving it is trivial:
[tex]\dfrac{\mathrm dy}{\mathrm dt}=ky\implies\dfrac{\mathrm dy}y=k\,\mathrm dt[/tex]
Integrating both sides gives
[tex]\ln|y|=kt+C\implies y=e^{kt+C}=Ce^{kt}[/tex]
Given [tex]y(0)=24[/tex] and [tex]y(1)=18[/tex], we find
[tex]24=C[/tex]
[tex]18=Ce^k=24e^k\implies e^k=\dfrac34\implies k=ln\dfrac34[/tex]
so the answer is E.
Answer:
E
Step-by-step explanation:
dy/dt = ky
1/y .dy = k .dt
ln(y) = kt + c
t = 0, y = 24
ln(24) = 0 + c
c = ln(24)
ln(y) = kt + ln(24)
t = 1, y = 18
ln(18) = k + ln(24)
k = ln(18) - ln(24)
k = ln(18/24) = ln(3/4)