To find the product of \((f+1)(f+3)\), we can use the distributive property (also known as the FOIL method for binomials).
-
First: Multiply the first terms:
\[ f \cdot f = f^2 \] -
Outer: Multiply the outer terms:
\[ f \cdot 3 = 3f \] -
Inner: Multiply the inner terms:
\[ 1 \cdot f = f \] -
Last: Multiply the last terms:
\[ 1 \cdot 3 = 3 \]
Now, we can combine all these results:
\[
f^2 + 3f + f + 3
\]
Next, combine the \(3f\) and \(f\) terms:
\[
f^2 + 4f + 3
\]
So, the simplified product of \((f+1)(f+3)\) is:
\[
\boxed{f^2 + 4f + 3}
\]