∵27²=（3³）²=3^6=(3²)³=a^6=9^b
∴a=3,b=3
[a-五分之一乘b]的2次方+[a+五分之一乘b]的2次方+2b[a-25分之一乘b]
=a²-(2/5)ab+(1/25)b²+a²+(2/5)ab+(1/25)b²+2ab-(2/25)b²
=2a²+2ab
当a=3,b=3时,
原式=2×3²+2×3×3
=18+18
=36