1.[(a+b)²-3ab][(a-b)²+3ab]2.(x+y+z)(x+y-z)-(x-y+z)(x+y-z)3.已知x=2,y=-4时,代数式ax³+1/2by+5=1997,当x=-4,y=-2时,求代数式3ax-24by³+4986的值.

1.[(a+b)²-3ab][(a-b)²+3ab]2.(x+y+z)(x+y-z)-(x-y+z)(x+y-z)3.已知x=2,y=-4时,代数式ax³+1/2by+5=1997,当x=-4,y=-2时,求代数式3ax-24by³+4986的值.
1.[(a+b)²-3ab][(a-b)²+3ab]
2.(x+y+z)(x+y-z)-(x-y+z)(x+y-z)
3.已知x=2,y=-4时,代数式ax³+1/2by+5=1997,当x=-4,y=-2时,求代数式3ax-24by³+4986的值.

1.[(a+b)²-3ab][(a-b)²+3ab]2.(x+y+z)(x+y-z)-(x-y+z)(x+y-z)3.已知x=2,y=-4时,代数式ax³+1/2by+5=1997,当x=-4,y=-2时,求代数式3ax-24by³+4986的值.
1.[(a+b)²-3ab][(a-b)²+3ab]
=[a^2+b^2-ab][a^2+b^2+ab]
=(a^2+b^2)^2-(ab)^2
2.(x+y+z)(x+y-z)-(x-y+z)(x+y-z)
=(x+y-z)[(x+y+z)-(x-y+z)]
=(x+y-z)(2y)
=2y(x+y-z)
3.已知x=2,y=-4时,8a-2b+5=1997
x=-4,y=-2时,-64a-b+5=1997
得到：a=,b=

1.[(a+b)2-3ab][(a-b)2+3ab]
=(a2+b2-ab)(a2+b2+ab)
=(a2+b2)2-a2b2
=a4+b4+a2b2
2.(x+y+z)(x+y-z)-(x-y+z)(x+y-z)
=[(x+y)2-z2]-[x2-(y-z)2]
=x2+y2+2xy-z2-(x2-y2-z2+2yz)
=2y2+2xy-2yz
字母后面的数字表示次方，打不来。
第三题不会了