Question

If y=e3t is a solution to the differential equation

d2ydt2−9dydt+ky=0,
find the value of the constant k and the general solution to this equation.​

Answer 1

k=18, general solution does not exist.

Explanation:

If f(t)=y=e3t is a solution to the differential equation

d2ydt2−9dydt+ky=0,

then

y = e^(3t)

y' = dy/dt = 3y

y'' = d2ydt2 = 9y

y'' - 9y' + ky = 0

9y - 9(3y) + ky = 0

(9-27+k)y = 0

solve for y

(9-27+k) = 0

k = 18

general solution is when y=e^(3t)=0, or t-> -infinity