"Amitava" wrote...
I tried to create equations from the set of data by solver
x= 90021 85248 78314 69768 59508 47975
y = 20.09 19.92 18.70 16.95 16.13 15.67

in the form of y= a + bx +cx2 + dx3;
where x2= x square ,x3 = x cube.

but could not do so.
the solver does fine when the value of x is small .
Your help will be hghly appreciated in this regard.

In Excel you're limited to 15 decimal digit precision most of the time. A
few intermediate calculations may have more if they can stay in FPU
registers. However, standard minimizing sum squared error fitting would at
some point involve squaring the x^3 values, at which point you've blown way
past machine precision.

That said, plot these X-Y values in an X-Y chart, add a polynomial trend
line or order 3, and display the trend line equation. It'll show the a, b, c
and d coefficients you seek.