...
End With
DL = Range("A65500").End(xlUp).Row
Set MatX = Range("A2:A" & DL)
Set MatY = Range("B2:B" & DL)
[F2] = WorksheetFunction.LinEst(MatY, MatX)
[F2].Offset([0], [1]) = WorksheetFunction.Index(WorksheetFunction.LinEst(MatY, MatX), 2)
Dim a
...