x²+mx+4=0①和x²-(m-2)x-16=0②有一个相同的根,①-②,（2m-2)x+20=0,x=10/(1-m),③代入①,100/（1-m)^2+10m/(1-m)+4=0,两边都乘以（1-m)^2/2,得50+5m(1-m)+2(1-m)^2=0,50+5m-5m^2+2-4m+2m^2=0,52+m-3m^2=0...