Question

Without solving for the undetermined coefficients, the correct form of a particular solution of the differential equation y'' + 9y = sin(3x) is:_______

a. yp = Acos(3x) + Bsin(3x)
b. yp = Axcos(3x) + (3x)
c. yp = Asin(3x)
d. yp = Acos(3x)
e. yp = Axcos(3x) + Bxsin(3x)

Answer 1

E

Explanation:

y’’ + 9y = sin(3x)

The characteristics equation is;

m^2 + 9 = 0

solving this we have 2 complex roots

m= -3i, 3i

Thus;

yh = Ccos(3x)+ Dsin(3x)

let yp = Axcos(3x) + Bxsin(3x)

Now, because we have sin(3x) and cos(3x) with constant coefficient in yh, option E is our answer