First I looked for a linear twovariable function that fit the given data, namely a function f[x,y]=a*x+b*y+c for some a,b,c that would exactly fit the given data points. Since that failed I increased the degree by 1 to include all second degree combinations of variables x,y namely
f(x,y)=a*x+b*y+c*x^2+d*y^2+e*x*y+f
I was able to find one that exactly fits the data points namely
f(x,y)=(309387967984  39145241276 x  434958311 x^2 + 10320649220 y +
10959785095 x y  10241576646 y^2)/9608523792
using this we get f(7,11)=44623643103/1601420632
or approximately 27.865

Posted by Daniel
on 20170513 13:25:31 