Help in curve fitting tool

I've a curve(x and y values) and I've to apply following custom equation and have to find the unknown parameters A and B

y=3.379-(A*X^2/(B+X))

I'm using the Cftool and using the custom equation button but what I see there is not any option(or it appears to me) of entering the above equation I've mentioned. Please guide me how to fix this issue.

Answer 1

[Andreas Goser]

Things that could go wrong

• The user does not see the tab "general equations" when creating a new fit
• Issues with variable / parameter names like upper and lower case x
• Equation not correct with regards to operators - .* vs *, .^ vs ^ and so on
• Last not least it could be that your data just does not match...