limx→∞[(2x-1)^30(3x-20)^20/(2x+1)^50
=lim [(2x-1)/(2x+1)]^30* [(3x-20)/(2x+1)]^20
=lim [(2-1/x)/(2+1/x)]^30* [(3-20/x)/(2+1/x)]^20
=1*（3/2）^20
=（3/2）^20