How to have a cell A equal cell B IFERROR in cell C OR cell D, but empty if cell C isn't an error?

[MirohLoome]

My issue is that I want to have cell E11 equal to cell E8 if cell I8 is an error, but have cell E11 be empty if cell I8 ISN'T an error. I have tried using various combinations of IFERROR and IF functions, but cant come up with a solution. I know basic excel functions but cant figure out some of the more complex ones and when/how to use them. I am trying to make a calculator that outputs all possible answers and stages of simplification of a simple ax^2+bx+c equation, so I am also trying not to mess up my other formulas in the process. Any suggestions? Here is my sheet for reference. Any tips on any of the other parts of the sheep would be great too.

synthetic division calculator.xlsx

[#2]

*sheet not sheep 💀

[#3]

@MirohLoome 

=IF(ISERROR(I8),E8,"")

[#4 · Accepted solution]

@MirohLoome 

In E11:

=IF(ISERROR(I8), E8, "")

This will cause a problem with F12, so change the formula there to

=IF(E11="", "", E11/(D12^2)*-1)

[#5]

Perfect! Thanks for also helping with the error in F12! You are awesome!

[#6]

Also: I haven't found any way to do the opposite of IFERROR, eg. ifNOTerror. I would like to have a formula similar to the one @HansVogelaar mentioned in cell E15, but IFERROR should be reversed in some way. Is there any way to do this?

[#7]

@MirohLoome

=IF(NOT(ISERROR(something)), value_if_no_error, value_if_error)

[#8]

@HansVogelaar 

Sorry, one more thing (i hope.) I want to enter the largest whole number of a set of numbers that include decimals (specifically the largest whole number from P4:P54 entered into D16) and also possibly fix the repeating zeros in P4:P54 but still calculate the square root of the factors in O (eg. only calculate the factors until the last number in O then leave the rest of P blank)

Thanks so much for all your help so far!

[#9]

@MirohLoome 

In P3 (not P4):

=SQRT(O3#)

In D16:

=MAX(IF(MOD(P3#, 1)=0, P3#))