求a=b=c的值求AB:BM的值.
(1)若a:b:c=3:5:7,且3a+2b-4c=9,且3a+2b-4c=9,求a=b=c的值.(2)已知M是线段AB延长线上一点,且AM:BM=5:2,求AB:BM的值.