1.oa=1km,ab=160m,所以OB=840M用公梁慧式y=a(x+m)^2+by=a(x-0)^2+1000840=a(200)^2+1000a=-1/250y=-1/250x^2+10000=-1/250x^2+1000x^2=250000x=500 第银碧二问,字母是不是标错了,锋渣举没看明白