a+b=3²=9 (1)
a-b=3³=27 (2)
(1)+(2)
2a=36 a=18
(1)-(2)
2b=-18 b=-9
±⁴√(2a-5b)=±⁴√[2×18-5×(-9)]
=±⁴√81
=±3
2a-5b的四次方根为3或-3.