a^2+3a+1=0
把a=1代入,1=0,不成立,所以a不等于0
所以a+3+1/a=0
(1)a+1/a=-3
(2)(a+1/a)^2=a^2+2+1/a^2=9
所以a^2+1/a^2=7
(3)(a^2+1/a^2)^2
=a^4+2+1/a^4=49
所以a^4+1/a^4=47
(2x+3xy-2y)/(x-2xy-y)
=[2(x-y)+3xy]/[{x-y)-2xy]
=(2*4xy+3xy)/(4xy-2xy)
=11/2
a/3=b/5=c/7
所以a=3c/7,b=5c/7
3a+2b-4c=9c/7+10c/7-4c=-9c/7=9
c=-7
a=-3,b=-5
a+b+c=-15