1.若abc不等於0.且3a-2b+6c=0.則(b+2c)/a=?
2.la-2bl+lb-3cl=0.且3a-2b-5c=21.則a+b+c=? PS: l l(絕對值)
3.若(a-1):(b-2):(c+5)=5:6:4,a+b=1+3c,則a.b.c的值為何?