x=2,y=-4,代数式ax的三次方+二分之一by+5=1997
a*2^3+1/2*b*(-4)+5=1997
8a-2b=1992
4a-b=996
当x=-4,y=负二分之一时,
3ax-24by的三次方+4986
=3a*(-4)-24*b*(-1/2)^3+4986
=-12a+3b+4986
=-3(4a-b)+4986
=-3*996+4986
=1998
x=2,y=-4,代数式ax的三次方+二分之一by+5=1997
a*2^3+1/2*b*(-4)+5=1997
8a-2b=1992
4a-b=996
当x=-4,y=负二分之一时,
3ax-24by的三次方+4986
=3a*(-4)-24*b*(-1/2)^3+4986
=-12a+3b+4986
=-3(4a-b)+4986
=-3*996+4986
=1998