ax^2+bx+c=0(1)两根互为倒数的条件是:x1*x2=1,c/a=1,a=c(2)两根互为相反数的条件是:x1+x2=0,-b/a=0,b=0(3)两根异号的条件是:x1*x20(5)两根都是正数的条件是:x1*x2>0,x1+x2>0c/a>0,-b/a>0(6)两根负数的条件是:x1*x2>0...