Does anyone have a suggestion of how I can enter the following array formula
into Excel in a much simpiler way?

=INDEX(LINEST(TaveRNG,TimeRNG^{1,2,3}),1)*Time^3+I NDEX(LINEST(TaveRNG,TimeRNG^{1,2,3}),2)*Time^2+IND EX(LINEST(TaveRNG,TimeRNG^{1,2,3}),3)*Time+INDEX(L INEST(TaveRNG,TimeRNG^{1,2,3}),4)

To explain:
LINEST(TaveRNG,TimeRNG^{1,2,3}) returns an array of coefficients {a,b,c,d}
for my curve fit
y = a*x^3 + b*x^2+c*x+d

I have a feeling that this could be entered into excel something like:
=SUM(LINEST(A1:A10,B1:B10^{1,2,3})*{B1^3,B1^2,B1,1 })
except I can't build an array between brackets { } with a reference to a
cell, this only works with constants.

Do I need to create a custom UDF to handle something like this?