15 ! решите уравнение : (x^2-8)^2+4 (x^2-8)-5=0

( x^2 - 8 )^2 + 4( x^2 - 8 ) - 5 = 0
X^2 - 8 = a
a^2 + 4a - 5 = 0
D = 16 + 20 = 36 = 6^2
a1 = ( - 4 + 6 ) : 2 = 1
a2 = ( - 4 - 6 ) : 2 = - 5
1) x^2 - 8 = 1
x^2 = 9
X1 = 3
X2 = - 3
2) x^2 - 8 = - 5
X^2 = 3
X1 = V 3
X2 = - V 3