1.=(64+4)/(-27)=-68/27
2.=5a^2-[a^2-(a^2+2a+5a^2-2a^2+6a)]
=5a^2-(a^2-4a^2-8a)
=5a^2+3a^2+8a
=8a(a+1)
3.6x-24x-2=6-4x
14x=-8
x=-4/7
4.1-4/5(-x+2)-8+1=0
5+4x-8-35=0
4x=38
x=19/2
5.y/2+x/3=13(1)
y/3-x/4=3(2)
(1)*2-(2)*3得
17/12*x=17
x=12
代入(1)得：y=18
6.x/2+y/3=2(1)
2x+3y=28(2)
(2)-(1)*4得
5/3*y=20
y=12
代入(2)得：x=-4