Concept:
The complementary function is obtained from the homogeneous part of the differential equation.
Given,
\[
(D-2)^2y=8e^{-x}
\]
For complementary function, we solve
\[
(D-2)^2y=0
\]
Step 1: Write the auxiliary equation.
Replace \(D\) by \(m\):
\[
(m-2)^2=0
\]
Step 2: Find the roots.
\[
(m-2)^2=0
\]
\[
m=2,2
\]
So \(m=2\) is a repeated root.
Step 3: Write the complementary function.
For repeated root \(m\), the complementary function is
\[
(c_1+c_2x)e^{mx}
\]
Here,
\[
m=2
\]
Therefore,
\[
C.F.=(c_1+c_2x)e^{2x}
\]
Step 4: Final answer.
\[
\boxed{(c_1+c_2x)e^{2x}}
\]