Question : quadratic equation: Keep getting 1 answer right, the other one won't match up

The problem is:
4y^2 = 5 - y^4

The following is how far I got:
y^4 + 4y^2 - 5 = 0

A = 1 B = 4 C = - 5

( -4 +/- sqrt(4^2 - 4*1*-5) ) / 2(1)

After breaking that down further, I got to:

( -4 + 6 ) / 2
OR
( -4 - 6 ) / 2

Which gives me: y = 1 OR y = -5

The book and my TI-89 however, disagree. The answer should be y = 1 OR y = -1

... Help?

Answer : quadratic equation: Keep getting 1 answer right, the other one won't match up

(y^2)^2 + 4(y^2) - 5 = 0
Which gives me: (y^2) = 1 OR (y^2) = -5