Easy Limit

Find the limit as x tends to negativeinfinity
(Square root of (4x^(2) + 1) ) / (4x+1)
I get 1/2, but my textbook ans is -1/2
Thank you
Sol
lim(x->－∞)_√(4x^2+1)/(4x+1)
=lim(y->∞)_√(4y^2+1)/(－4y+1)
=lim(y->∞)_√(4+1/y^2)/(－4+1/y)
=√4/(─4)
=－1/2