*** 注意:"m2" 在下面代表m的二次方,因为百度不能显示所以只能这样打出来了.
move the term such that:
x=(21m-9m2)/(-9m2-7)
x0
m(9m-21)>0
m(3m-7)>0
(m>0 and 3m-7>0) or (m7/3) or (m