Math help please!!!

Expand the left hand side

$abx^2+(a^2+b^2)x+ab=26x^2+[]x + 26$

So we must have 

a*b = 26

a and b are integers, so the possibilities are 

a = 1   b = 26

a = 2   b = 13    

(or the same with a and b switched).

Hence [] must be either $1^2+26^2$   or  $2^2+13^2$

I'll leave you to decide which is smaler.

Don't keep repeating the same question several times within a short period of time!