for question 4
we are trying to find
as we know f(x+3) is basically f(x) shifted 3 units to the left, hence we can say that
or we can use the substitution u=x+3 to show the same thing
now we can split
into
using that identity given we can evaluate that
to find
we have to use the fact that f(x) is odd, which means that
you can also get this result by using the substitution u=-x
thus
therefore