(5-а)(5+а)(25+а²)+(6+а²)²=

=(25-а^2)(25+а^2)+(36+12а^2+а^4)=

=625-а^4+36+12а^2+а^4=

=12а^2+661

если а=1/3

12*(1/3)^2+661=12*1/9+661=4/3+661=661 4/3=662 1/3