Hints for problem 8.4

 Assuming a B-spline smoother, we have that \(\hat{\boldsymbol{y}} = \boldsymbol{H}(\boldsymbol{H}^T\boldsymbol{H})^{-1}\boldsymbol{H}^T\boldsymbol{y}\), where \(\boldsymbol{H}\) is a B-spline basis matrix.