Example 1.7
Solve the following first order ODE:
2 3x
u − 3u = 3x e , u(0) = 1. (1.29)
Notice that p (x) = −3 and q(x) = 3x2e3x . The integrating factor μ(x) is
obtained by
x −3dt −3x
μ(x) = e 0 = e . (1.30)
Consequently, u(x) is obtained by using
1 x 3x x 2
u(x) = μ(t)q(t)dt + c = e 3t dt + c
μ(x) (1.31)
= e3x x3 + c = e3x (x3 + 1),
obtained upon using the given initial condition.