If limx→∞ f(x) exists and is finite and nonzero and if limx→∞ fx+3fx-1f2x=3, then the value of limx→∞ f(x) is ________
limx→∞ fx+3fx-1f2x=3 or limx→∞ fx+3limx→∞ fx-1limx→∞ fx2=3 or y+3y-1y2=3 (where y=limx→∞ fx) or y3-3y2+3y-1=0 or y-13=0 or y=1