Consider the following code:
In[1]
eqn = f2[w] == A + (\[Lambda]/k*\!\(
\*SubsuperscriptBox[\(\[Integral]\), \(Q\), \(w\)]\(
\*SuperscriptBox[\(e\), \(\(-\[Mu]\)*\((t - w)\)\)]*
f2[t] \[DifferentialD]t\)\));
sol = DSolveValue[eqn, f2[w], w]
But I got this answer
Out[2]
A + (\[Lambda] \!\(
\*SubsuperscriptBox[\(\[Integral]\), \(Q\), \(w\)]\(\(
\*SuperscriptBox[\(e\), \(\((\(-t\) + w)\)\ \[Mu]\)]\ f2[
t]\) \[DifferentialD]t\)\))/k
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