4. What does the inverse transform look like?

idct = Inverse[dct]

RowBox[{{, RowBox[{RowBox[{{, RowBox[{0.25, ,, 0.46194, ,, 0.353553, ,, 0.191342}], }}], ,, Ro ... Box[{{, RowBox[{0.25, ,, RowBox[{-, 0.46194}], ,, 0.353553, ,, RowBox[{-, 0.191342}]}], }}]}], }}]

%//MatrixForm

( 0.25` 0.46193976625564337` 0.35355339059327373` 0.1913417161 ... 0.25` -0.46193976625564337` 0.3535533905932738` -0.19134171618254492`

idct . {12, 0, 0, 0}

RowBox[{{, RowBox[{3., ,, 3., ,, 3., ,, 3.}], }}]

Created by Mathematica  (April 1, 2004)